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THE 


HUNT  AND  DOUGLAS  PROCESS 


FOR 


EXTRACTING  COPPER  FROM  ITS  ORES. 


WITH  AN  APPENDIX 


INCLUDING 


NOTES  ON  THE  TREATMENT  OF  SILVER 
AND  GOLD  ORES, 


AND    A    PLATE. 


BOSTON: 
PRESS  OF  A.  A.  KINGMAN. 

1876. 


H      . , 

THE 


HUNT  AND  DOUGLAS  PROCESS 


FOR 


EXTRACTING  COPPER  FROM  ITS  ORES. 


WITH  AN  APPENDIX 


INCLUDING 


NOTES  ON  THE  TREATMENT  OF  SILVER 
AND  GOLD  ORES, 


AND    A    PLATE. 


BOSTON: 

PRESS  OF  A.  A.  KINGMAN. 
1876. 


//V 


. 
-  h!-y> 


TIT 


1 

1 


J'ltrrrcux,  


-.*/.* 


TABLE  OF  CONTENTS. 


INTRODUCTION:  Wet  and  Dry  Processes  of   Copper  Extraction     .  5 

The  Hunt  and  Douglas  Process  ;  Working  Directions        .         .  6 

I.     Grinding  the  Ore         ........  7 

II.     Calcining  the  Ore        ........  8 

III.  Dissolving  the  Copper         .         .         .         .         .         ...  12 

IV.  Precipitating  the  Copper     .         .         .         .         .         .         .  17 

V.     Melting  and  refining  the  Copper          .         .         ...         .  18 

VI.     Arrangement  of  the  Plant  .  19 


APPENDIX. 

1.  Assaying  for  Copper  and  for  Iron        .....  20 

II.  Preparation  and  use  of  Iron  Sponge  ......  24 

III.  Use  of  Tin  Plate  Scrap 27 

IV.  Chemistry  of  the  Hunt  and  Douglas  Process       ...  28 
V.  Patent  Specification 33 

VI.  What  Ores  may  be  treated  by  the  Process           ...  34 

VII.  Practical  Working  of  the  Process 35 

VIII.  The  Treatment  of  Silver  and  Gold  Ores    .  37 


M342440 


THE 


HUNT  AND  DOUGLAS  COPPER  PROCESS. 


This  is  what  is  technically  called  a  wet  method,  because  the 
copper  is  removed  from  its  ores  in  a  dissolved  state,  the  sol- 
vent employed  in  the  present  process  being  a  watery  solution  of 
neutral  protochlorid  of  iron-  and  common  salt.  Most  oxydized 
compounds  of  copper —  whether  obtained  artificially  by  roasting 
sulphuretted  ores,  or  found  in  nature  in  the  forms  of  carbonates 
and  oxyds,  —  when  digested  with  such  a  solution  are  converted 
into  a  mixture  of  protochlorid  and  dichlorid  of  copper,  which  are 
dissolved,  while  the  iron  of  the  solvent  separates  in  the  form  of 
insoluble  hydrous  peroxyd  of  iron.  When  the  solution  of  the 
chlorids  of  copper  thus  obtained  is  brought  in  contact  with  me- 
tallic iron  the  copper  is  separated  in  a  metallic  crystalline  state, 
while  the  iron  passes  into  solution,  reproducing  the  protochlorid 
of  iron;  thus  restoring  its  solvent  powers  to  the  liquid,  wrhich 
we  shall  call  "  the  bath,"  and  fitting  it  for  the  treatment  of  a 
fresh  portion  of  copper  ore.  This  process  of  solution  and  pre- 
cipitation can,  under  proper  conditions,  be  repeated  in  efinitely 
with  the  same  bath,  the  only  reagent  consumed  being  the 
metallic  iron. 

The  chief  advantage  which  wet  processes  possess  over  smelt- 
ing lies  in  the  economy  of  fuel.  To  extract  copper  from  a  low 
grade  ore  by  smelting,  five  or  six  furnace-operations  are  neces- 
sary, and  about  one  ton  of  coal  is  consumed  for  each  ton  of  ore 
treated ;  while  for  the  various  wet  processes  a  single  calcination, 


6 

in  which  not  more  than  three  hundred  weight  of  coal  is  con- 
sumed for  each  ton  of  ore,  is  the  only  furnace-operation  required 
to  obtain  the  metallic  copper  in  a  precipitated  form  known  as 
cement  copper.  An  important  item  of  cost  in  wet  processes  is 
the  metallic  iron  employed  to  separate  the  metallic  copper  from 
its  solutions.  The  same  amount  of  iron  is  required  to  pre- 
cipitate a  ton  of  copper  whether  extracted  from  a  poor  or  a  rich 
ore,  but  as  for  the  smelting  of  the  latter  much  less  fuel  is 
required,  it  follows  that  rich  ores  are  generally  treated  by  smelt- 
ing rather  than  in  the  wet  way,  any  saving  of  fuel  in  the  latter 
being  more  than  compensated  for  by  the  cost  of  iron.  No  gen- 
eral rule  however  can  be  laid  down  to  determine  what  grade  of 
ore  can  be  more  profitably  treated  by  one  method  or  the  other, 
inasmuch  as  circumstances  of  locality,  affecting  the  cost  of  fuel 
and  the  price  of  iron,  must  in  each  case  be  taken  into  account. 
The  various  other  wet  methods  of  copper-extraction  may  be 
divided  into  two  classes  :  those  in  which  the  previously  oxydized 
ore  is  treated  with  hydrochloric  or  sulphuric  acid  to  dissolve  the 
oxyd  of  copper,  and  those  in  which  sulphuretted  ore,  generally 
after  a  preliminary  roasting,  is  calcined  with  an  admixture  of 
sea- salt  or  of  sulphate  of  soda,  by  which  the  copper  is  converted 
into  chlorid  or  into  sulphate.  All  of  these  methods,  when 
properly  applied,  effect  a  pretty  thorough  extraction  of  the 
copper,  but  the  cost  of  the  reagents  which  have  to  be  added  to 
every  charge  of  ore,  preclude  altogether  the  use  of  some  of 
these  methods,  except  in  certain  favored  localities,  and  render 
them  in  almost  all  cases,  it  is  believed,  less  economical  than  the 
present  one  with  the  Hunt  and  Douglas  bath,  for  which  the 
following  advantages  are  claimed : 

I.  It  is  a  general  method  adapted  to  all  compounds  of  copper, 
while  that  by  calcination  with  salt  is  only  applicable  to  sulphur- 
etted ores. 

II.  It  does  not  require  the  addition  of  reagents  such  as  acids, 
salt  or  sulphate  of  soda  to  each  charge  of  ore,  since  in  the  regular 
course  of  the  operation  the  solvent  required  for  the  treatment 
of  the  ore  is  constantly  reproduced. 


III.  The  bath  employed  being  neutral,  certain  impurities  of 
the   ore,  such   as   arsenic,  which  pass  into   solution    and  con- 
taminate the  product  in  the  wet  processes,  remain  undissolved, 
so  that  a  purer  copper  is  obtained. 

IV.  As  the  solution  obtained  is  neutral  and  free  from  per- 
salts  of  iron,  there  is   no  unnecessary  waste  or  consumption  of 
metallic  iron  in  the  process  of  precipitation.     Moreover,  as  the 
result  of  the  action  of  the  protochlorid  of  iron   of  the  bath  on 
protoxyd  of  copper,  one-third  of  the  copper  is  obtained  as  pro- 
tochlorid, and  two-thirds  as  dichlorid.     Now  since  the  latter 
requires  for  each  one  hundred  parts  of  copper  precipitated  only 
forty-five  parts  of  iron,  it  is  found   in  practice  that  not  more 
than  three-quarters  of  a  ton  of  iron  are  consumed  to  precipitate 
one  ton  of  metallic  copper,  while  in  the  other  methods,  in  which 
the  copper  is  obtained  as  protochlorid,  the  consumption  of  iron 
amounts  to  a  ton,  and  in  many  cases  greatly  exceeds  it. 


WORKING    DIRECTIONS. 

The  application  of  the  Hunt  and  Douglas  process  to  the  treat- 
ment of  copper  ore  may  be  considered  under  the  following 
heads : 

I.     Grindino-  the  ore. 

£5 

II.     Calcining  the  ore. 

III.  Dissolving  the  copper. 

IV.  Precipitating  the  copper. 

V.     Melting  and  refining  the  copper. 
VI.     Arrangement  of  the  plant. 

I.  Grinding  the  Ore.  The  degree  of  fineness  to  which  the 
ore  must  be  ground  will  depend  entirely  upon  the  character  of 
the  gangue.  If  the  metal  be  scattered  in  fine  particles  through 
an  impermeable  rock,  it  will  be  necessary  to  grind  it  to  the  size 
of  sand,  so  that  the  copper,  if  a  sulphuret,  may  be  exposed  to 
the  oxydizing  action  of  the  air  during  calcination,  and  to  the 
solvent  action  of  the  protochlorid  of  iron  bath  during  lixiviation. 


8 

If,  on  the  contrary,  the  eopper-fulphuret  be  mixed,  as  is  often  the 
case,  with  iron  pyrites,  which  by  calcination  becomes  porous,  the 
mv  need  not  be  ground  so  fine.  Experiment  in  each  case  must 
determine  the  point,  and  upon  the  decision  must  depend  the 
machinery  which  should  be  chosen  to  effect  the  grinding;  — 
Cornish  rolls  being  preferable  for  coarse  crushing  and  stamps 
for  finer  work.  Two  pairs  of  rolls,  —  one  pair  of  24  or  30 
inches  diameter,  and  one  pair  of  12  or  15  inches,  with  a  screen 
between  them  to  sift  out  what  is  not  broken  sufficiently  fine  by 
the  upper  pair,  will  crush  about  twenty  tons  of  stuff  in  twenty- 
four  hours  so  that  it  will  pass  through  a  sieve  of  fifteen  holes  to 
the  linear  inch,  ;i  degree  of  fineness  sufficient  for  most  ores.  A 
rock-breaker  with  jaws  set  close  may  be  substituted  for  the 
upper  pair  of  rolls. 

II.  Calcining  the  Ore.  It  is  not  necessary  to  calcine  car- 
bonates or  protoxyds,  but  mixtures  in  which  there  is  a  large 
proportion  of  red  or  dinoxyd  need  a  slight  roasting  to  convert 
at  least  a  part  of  this  into  protoxyd  ;  while  all  sulphuretted  ores 
require  much  more  calcination.  The  mode  of  effecting  this  will 
vary  with  the  character  of  the  ore.  When  it  contains  20  p.  c. 
or  upward  of  sulphur,  it  may  be  broken  into  lumps  of  an  inch 
or  more  in  diameter,  and  exposed  to  a  preliminary  roasting  in 
heaps  or  kilns,  whereby,  without  the  aid  of  fuel,  the  greater 
part  of  the  sulphur  will  be  driven  off,  and  the  metallic  ingre- 
dients more  or  less  completely  oxydized.  The  lumps  thus 
partially  roasted  should  then  be  crushed  and  calcined  in  a  muffle 
or  reverberatory  furnace.  The  calcination  of  all  ores  in  an 
earthy  gangue  must  be  effected  wholly  in  such  furnaces. 

The  first  rule  in  roasting  is  to  expose  the  ore  at  the  beginning 
to  a  low  heat,  which  is  to  be  gradually  increased  as  the  sulphur 
is  driven  oil'.  If  the  temperature  be  too  high  at  the  commence- 
ment of  the  operation,  the  ore,  if  highly  sulphuretted,  may 
become  softened  and  agglutinated  or  fritted,  after  which  it  is 
impossible  to  effect  a  proper  roast.  But  even  if  this  should  not 
happen,  too  high  a  heat  at  first,  or  indeed  at  any  stage  of  the 
process,  brings  the  copper  into  a  condition  in  which  it  is  diffi- 


9 

cultly  soluble  in  the  bath.  A  long  furnace  is  more  easily 
managed  than  a  short  one,  since  in  the  former  the  fire  can 
always  be  kept  strong  and  the  ore  moved  forward  from  a  cooler 
to  a  hotter  portion,  while  in  a  short  furnace  the  gradation  of 
heat  can  only  be  attained  by  close  attention  to  the  firing. 

A  long  muffle  furnace  always  gives  a  good  roast,  as  the  tile 
floor  protects  the  ore  from  excessive  heat,  and  there  is  sure  to 
be  an  oxydizing  atmosphere  in  the  furnace,  which  is  not  always 
the  case  in  a  reverberatory,  where  the  flame  comes  in  contact 
with  the  ore.  But  the  construction  of  the  muffle  furnace  is' 
expensive,  and  a  cheap  and  efficient  furnace  is  a  three-hearth 
reverberatory.  When  a  number  of  such  furnaces  are  needed, 
they  may  be  built  side  by  side,  in  a  row,  the  rabbling-doors 
opening  before  and  behind,  and  the  arches  of  the  whole  row 
being  supported  by  a  stone  buttress  at  each  end,  —  the  only 
binding  necessary.  The  fire-boxes  of  adjacent  furnaces  are 
placed  side  by  side.  The  dimensions  which  have  been  found 
advantageous  for  these  furnaces  are  as  follows  :  lower  hearth 
ten  feet  wide  by  sixteen  feet  long ;  upper  hearths  twelve  feet 
wide  by  fifteen  feet  long.  The  lower  hearth  is  contracted  in 
width  by  the  fire-place,  and  the  upper  hearths  in  length  by  the 
flues  which  lead  from  hearth  to  hearth.  The  details  of  con- 
struction are  shown  in  the  accompanying  plan. 

The  advantages  of  such  a  form  of  furnace  are  cheapness  of 
construction  and  economy  of  heat,  on  account  of  the  exposure  of 
a  less  amount  of  cooling  surface  than  in  the  long  reverberatory 
with  rabbling-doors  on  the  side.  On  the  other  hand  the  upper 
hearths  are  not  very  accessible  to  the  rabblers.  If  such  a 
furnace  be  used,  the  heat  should  only  be  sufficient  to  thoroughly 
dry  and  warm  the  ore  on  the  uppermost  hearth.  Oxydation 
should  take  place,  with  the  elimination  of  the  greater  part  of  the 
sulphur,  on  the  second  hearth,  so  that  when  the  ore  is  exposed 
to  the  higher  temperature  of  the  lower  hearth  there  may  be  no 
danger  of  fritting.  The  quantity  of  ore  which  may  be  roasted 
in  such  a  furnace  will  depend  on  the  character  of  the  ore  and 
the  proportion  of  sulphate  of  copper  which  it  may  be  desirable 


10 

to  obtain.  If  the  ore  is  highly  sulphuretted  and  has  not  re- 
ceived a  preliminary  roast  hefore  grinding,  only  two  or  three 
tons  can  he  calcined  in  twenty-four  hours,  whereas  double  that 
quantity  may  be  treated  if  the  ore  be  poor  in  sulphur.  An  ore 
with  from  15  p.  c.  to  20  p.  c.  of  sulphur  maybe  added  in  charges 
of  2500  Ibs.  and  shifted  from  hearth  to  hearth  every  eight  hours, 
while  one  containing  from  5  p.  c.  to  7  p.  c.  of  sulphur  may  be 
shifted  every  five  hours. 

If  the  ore  contains  no  carbonate  of  lime  or  magnesia  (which 
will  deprive  the  bath  of  the  chlorid  of  iron  in  the  subsequent 
operation  of  solution),  the  roast  need  not  contain  over  one- 
fourth  of  its  copper  in  the  state  of  sulphate.  This  will  be  more 
than  sufficient  to  repair  unavoidable  losses  in  the  iron-chlorid  of 
the  bath.  The  presence  of  portions  of  these  obnoxious  ele- 
ments may,  however,  make  it  desirable  to  obtain  in  the  roast  a 
larger  proportion  of  sulphate  of  copper  (which  is  soluble  in 
water  and  by  its  precipitation  by  metallic  iron  yields  an  iron- 
salt).  To  obtain  this  the  ore  should  be  roasted  more  slowly 
and  in  larger  charges,  say  of  5000  Ibs.  each,  in  which  case  the 
yield  of  ore  from  the  furnace  will  be  somewhat  diminished. 

The  quantity  of  fuel  consumed  will  vary  with  the  different 
ores,  but  as  a  rule  one  cord  of  wood  will  suffice  for  three  tons, 
and  one  ton  of  coal  for  eight  tons  of  ore. 

When  a  sulphuretted  ore  has  been  properly  roasted  it  loses, 
when  being  rabbled,  that  apparent  fluidity  which  ore  still  giving 
off  sulphurous  acid  exhibits,  and  when  withdrawn  and  cooled 
should  have  a  bright  red  color.  If  the  heat  has  been  too  great 
the  color  of  the  cooled  ore  will  vary  through. dull  red  to  black. 
There  is  more  danger  of  having  too  much  than  too  little  heat 
in  the  furnace.  The  ore  on  the  upper  hearth  should  never  be 
in  a  glow,  and  that  on  the  lower  hearth  should  never  attain  a 
higher  heat  than  dull  redness.  Besides  regulating  the  heat,  it 
is  important  to  attend  to  the  admission  of  air.  As  the  roasting 
of  the  ore  is  an  oxydizing  process  an  abundance  of  air  is  es- 
sential to  the  operation,  and  that  this  may  be  supplied,  the 
furnace  must  possess  a  good  draft  and  be  provided  with  openings 


11 

sufficiently  large  and  numerous.  If  the  furnace  be  defective  in 
these  points  the  ore  will  be  scorched  and  its  copper  rendered 
insoluble  by  a  reducing  action  on  the  lower  hearth,  while  the 
upper  hearth  will  be  liable,  at  the  same  time,  to  become  too  hot. 

The  more  completely  the  sulphuret  of  copper  is  oxydized  in 
the  roasting,  the  more  thorough  will  be  the  subsequent  ex- 
traction of  the  copper,  but  to  oxydize  the  last  traces  of  sulphuret 
requires  a  disproportionate  expenditure  of  time,  labor  and  fuel. 
Upon  the  relative  value  of  the  raw  ore,  and  of  labor  and  fuel, 
will  therefore  depend  the  degree  of  thoroughness  to  which  it 
may  be  profitable  to  carry  the  extraction  of  the  copper  at  any 
given  reduction-works.  While  it  is  desirable  to  oxydize  as 
completely  as  consistent  with  economy  the  sulphurets  of  the 
ore,  it  should  be  borne  in  mind  that  a  dead  roast,  as  it  is  called, 
or  the  elimination  of  that  portion  of  sulphur  which,  after  oxy- 
dation,  remains  combined  as  sulphate  of  copper,  is  to  be  avoided, 
since,  as  already  pointed  out,  to  provide  for  unavoidable  loss  of 
chlorid  of  iron  it  is  desirable  to  leave  a  portion  of  sulphate  of 
copper  in  the  roasted  ore.  The  composition  of  the  roast  may 
be  seen  from  the  following  examples. 

At  the  Ore  Knob  Mine  in  North  Carolina,  the  average  of  the 
ore  roasted  by  this  process  was,  according  to  Mr.  Olcott,  (Trans. 
Amer.  Inst.  Min.  Engineers,  vol.  III.  p.  395.)  : 

Copper  as  sulphate     .         .         .         .         .         .         ,         3.76 

Copper  as  oxyd     ........     7.75 

Copper  as  sulphid .39 

11.90 

At  Phoenixville,  Pennsylvania,  where  the  ore  contains  a  con- 
siderable quantity  of  carbonate  of  magnesia,  the  effect  of 
which  has  to  be  neutralized  by  a  large  proportion  of  sulphate 
of  copper,  and  where  charges  of  5000  Ibs.  of  ore  are  calcined 
for  twenty-four  hours  on  each  hearth  of  the  dimensions  above 
given,  the  roasted  ore  has  the  following  average  composition  : 

Copper  as  sulphate     .         .         .         .         .         .         .         1.25 

Copper  as  oxyd 1.10 

Copper  as  sulphid .40 

2.75 


12 

For  the  method  of  determining  by  assay  the  composition  of 
the  roasted  ores,  see  Appendix,  p.  21. 

III.  Dissolving  the  Copper.  The  solvent  or  bath  employed 
for  the  extraction  of  the  copper  is,  as  has  been  stated,  a  neutral 
solution  of  protochlorid  of  iron  with  common  salt.  This  proto- 
chlorid  may  be  obtained  in  various  ways.  In  localities  where 
acids  are  cheap  it  is  easily  made  by  dissolving  scrap  iron  in 
diluted  muriatic  or  sulphuric  acid ;  the  first  yields  directly  pro- 
tochlorid, the  second  protosulphate  of  iron,  which  when  mixed 
with  a  solution  of  salt  gives  rise  to  the  protochlorid,  together 
with  a  portion  of  sulphate  of  soda.  In  places  where  acids 
are  not  so  easily  had,  the  commercial  protosulphate  of  iron 
(green  copperas)  is  the  most  convenient  source  of  the  proto- 
chlorid, as  explained  in  the  specification.  100  Ibs.  of  the 
commercial  acid  and  56  Ibs.  of  scrap  iron  will  make  280  Ibs. 
of  copperas.  Knowing  the  relative  cost  of  these  substances  at 
any  locality,  it  will  be  easy  to  calculate  whether  it  is  cheaper  to 
make  the  copperas  or  to  purchase  it.  Where  highly  sulphur- 
etted copper  ores  or  copper  pyrites  are  to  be  had  these,  by 
calcining  at  a  low  red  heat  (as  already  stated)  yield  large 
proportions  of  sulphate  of  copper  and  sulphate  of  iron,  both  of 
which  are  soluble.  By  leaching  these  roasted  ores  with  water 
and  digesting  the  solution  thus  obtained  with  scrap  iron  the 
dissolved  copper  is  thrown  down  as  metal,  and  a  solution  of 
protosulphate  of  iron  obtained,  which  may  be  mixed  with  salt 
to  form  the  bath. 

In  the  original  specification  of  the  process  it  was  directed  in 
making  the  bath  by  the  use  of  protosulphate  of  iron  to  take 
280  Ibs.  of  this,  (equal  to  56  Ibs.  of  metallic  iron)  and  120  Ibs. 
of  salt,  sufficient  to  convert  it  into  protochlorid.  These  dis- 
solved in  1000  Ibs.  of  water  (100  imperial  gallons)  with  a 
a  farther  addition  of  200  Ibs.  of  salt  made  the  strongest  bath, 
but  a  weaker  one  was  also  recommended  in  which  these  same 
ingredients  were  to  be  dissolved  in  2000  Ibs.  of  water.  Ex- 
perience has  shown  that  the  latter  is  strong  enough  for  the 
treatment  of  all  ordinary  ores. 


13 

The  bath  may  be  brought  in  contact  with  the  ore  either  by 
percolation  in  leaching  tanks,  or  by  agitation  in  vats  arranged 
with  stirrers.  If  the  ore  be  finely  ground  and  slimy,  the  latter 
must  be  used,  but  if  it  is  coarse,  and  contains  nothing  which 
when  wetted  will  form  mud,  it  is  best  treated  by  leaching. 
When  agitation  is  required  the  tanks  should  be  round,  ten  or 
twelve  feet  in  diameter,  and  five  or  six  feet  high,  and  made  of 
three-inch  staves.  A  convenient  stirring  apparatus  consists  of 
two  oblique  blades  fixed  to  the  base  of  a  vertical  shaft,  which 
rests  on  the  vertex  of  a  conical  bottom.  The  tips  of  the  blades 
should  reach  to  within  an  inch  of  the  sides  of  the  tank,  and  be 
raised  about  fifteen  inches  above  the  level  of  the  bottom  of  the 
tank  at  the  periphery.  The  object  of  thus  elevating  the  stirrer 
on  a  cone  above  the  bottom  is  to  permit  the  ore  to  settle  below 
the  blades,  so  that  the  stirrer,  after  having  been  stopped,  can  be 
started  at  will ;  whereas  were  the  bottom  flat  and  the  distance 
between  it  and  the  blades  the  same  at  all  points,  the  ore  would 
accumulate  around  the  shaft  and  thus  escape  agitation.  The 
stirrer  should  make  about  twenty  revolutions  a  minute.  A  vat 
of  the  above  dimensions,  having  a  capacity  of  about  3000  gal- 
lons, and  two-thirds  filled  with  bath,  will  serve  to  agitate  and 
dissolve  the  copper  from  3000  Ibs.  of  roasted  ore  containing  five 
or  six  p.  c.  of  copper  oxyd  in  six  to  eight  hours,  the  temperature 
being  from  120°  to  150°  F.  The  stirrers  are  then  stopped,  the 
whole  allowed  to  settle,  the  clear  liquor  drawn  off  into  the  pre- 
cipitating tanks,  and  the  muddy  portions  into  settling  tanks, 
after  which  the  residue  may  be  washed,  first  with  bath,  and  then 
with  water,  to  remove  the  adherent  copper  solution. 

When  percolation  can  be  adopted  it  is  preferable  to  stirring, 
since,  though  the  operation  is  slower,  we  are  enabled  to  dispense 
with  the  settling  tanks  which  the  latter  plan  requires,  and  the 
handling  of  the  slimes  which  accumulate  in  these.  Moreover, 
as  the  solution  of  the  copper  takes  place  in  the  mass  of  ore  out 
of  contact  of  air,  a  larger  proportion  of  dichlorid  of  copper  is 
found  and  less  iron  is  lost  by  oxydation  than  when  the  solution 


14 

holding  the  dissolved  iron  and  copper  salts  is  exposed  to  the  air 
by  constant  agitation. 

The  vats  for  filtration  are  made  of  wood  or  of  brick.  For 
the  latter  the  bricks  are  laid  in  Roman  cement  and  coated 
within  by  a  layer  of  the  same  cement  mixed  with  silicate  of 
soda.  This,  when  afterwards  washed  with  a  solution  of  chlorid 
of  calcium,  forms  a  coating  which  resists  the  action  of  the  metallic 
salts  of  the  bath.  If  wood  be  used  the  vats  may  either  be 
square  or  round,  but  in  any  case  they  should  be  somewhat 
wider  at  the  top  than  at  the  bottom,  otherwise  the  settling  and 
contraction  of  the  moistened  ore  will  leave  a  space  along  the 
walls  through  which  the  bath  may  descend  without  percolating 
the  mass.  Filtering  vats  need  not  be  more  than  three  feet  high. 
The  filter  may  be  made  by  laying  on  the  bottom  of  the  vat 
three  inches  of  small  stones,  broken  cinder  or  coke,  and  cover- 
ing this  by  a  layer  of  coarse  sand  upon  which  the  ore  may  be 
laid  to  the  depth  of  one  or  two  feet  according  to  its  coarseness 
or  fineness.  Instead  of  this  arrangement  a  false  bottom,  con- 
sisting of  perforated  planks  or  of  narrow  boards  loosely  laid 
ogether,  may  be  covered  over  with  coarse  sacking  upon  which 
the  ore  is  spread.  A  hole  in  the  side  near  the  bottom  of  the 
tank,  into  which  is  fitted  an  india-rubber  tube  provided  with 
a  squeezer  or  pinch-cock,  gives  vent  to  the  liquor  after 
its  passage  through  the  ore.  The  vats  should  be  fitted  with 
close  covers  so  as  to  exclude  the  air  and  retain  the  heat ;  these 
are  provided  with  a  small  hole  through  which  enters  a  tube  to 
supply  the  bath.  It  is  well  to  spread  the  ore  in  the  vats  already 
partially  filled  with  heated  bath,  as  when  thus  wet  down  it  will 
not  cake  but  will  permit  the  bath  to  percolate  uniformly  through 
it.  When  the  desired  quantity  of  ore  has  been  added  a  wooden 
float  should  be  secured  beneath  the  opening  in  the  cover  so  that 
the  bath,  as  it  flows  in,  may  fall  thereon,  otherwise  it  would 
make  a  depression  in  the  mass  and  thus  the  percolation  would 
be  unequal.  About  two  or  three  inches  of  bath  should  be  kept 
on  the  top  of  the  ore,  and  it  should  be  supplied  as  rapidly  as  it 
escapes  from  the  tube  below.  When  the  outflowing  liquid  is 


15 

found,  by  testing  with  a  bit  of  iron  wire,  to  contain  no  more 
copper  than  the  liquid  entering  above,  we  know  that  the  soluble 
copper  has  been  removed  and  it  only  remains  to  stop  the  supply 
of  bath,  allow  the  layer  above  to  filter  through  and  then  dis^ 
place  that  which  remains  in  the  pores  of  the  exhausted  mass  by 
the  addition  of  a  little  water.  The  extraction  of  the  copper  by 
filtration  may  not  be  completed  in  less  than  three  or  four  days* 
the  time  of  course  depending  on  the  richness  of  the  ore  and  the 
strength  and  the  temperature  of  the  bath. 

The  solution  of  the  copper  is  much  accelerated  by  heating 
the  bath,  which  may  be  done  by  the  injection  of  steam.  If  the 
liquid  be  heated  to  from  120°  to  180°  F.  it  will  flow  through  the 
ore  in  the  leaching  tanks  with  a  very  little  reduction  of  tempera- 
ture, and  the  heat  generated  in  the  process  of  precipitation  will,  if 
the  tanks  for  this  operation  are  well  covered,  maintain  the  bath 
in  these  at  a  sufficient  temperature  to  ensure  a  quick  separation 
of  the  copper,  so  that  it  is  only  the  liquid  in  the  store  tanks  that 
will  require  heating  by  steam. 

The  bath  after  it  is  withdrawn  from  the  precipitating  tanks 
generally  contains  a  little  copper.  If,  however,  care  be  taken 
to  leave  it  there  till  the  whole  of  the  copper  is  separated,  the 
liquid  will  then  be  without  action  on  metallic  iron,  and  steam 
coils  may  be  used  to  heat  it  in  the  store  tank,  or  in  passing  from 
this  to  the  leach  vats  it  may  be  made  to  pass  through  a  coil  of 
iron  pipe  heated  by  a  stove. 

Where  kilns  are  used  for  roasting,  the  heating  of  the  liquors, 
as  well  as  the  evaporation  of  the  excess  of  liquid  derived  from 
the  wash-waters,  may  be  effected  in  Gay-Lussac  towers,  which 
are  small  brick  or  stone  chambers,  tall  and  narrow,  filled  with 
fragments  of  coke  or  broken  bricks,  in  which  an  ascending 
current  of  the  hot  air  and  sulphurous  vapors  meets  a  descend- 
ing current  of  the  liquid.  The  hot  gases  from  the  kiln  or  from 
a  muffle  may  also  be  utilized  by  drawing  them  through  a  pipe 
from  four  to  six  inches  in  diameter  by  means  of  a  small  steam 
jet  introduced  at  the  bend  in  an  injection  pipe,  which  at  that 
point  should  be  contracted  to  two  inches,  and  may  dip  two  feet 


16 

or  more  into  the  liquid  in  the  store  tank.  Such  an  arrangement 
saves  steam  and  serves  to  impregnate  the  bath  with  sulphurous 
acid,  which  in  its  passage  through  the  ore  in  the  filtering  vats 
serves  to  attack  the  separated  peroxyd  of  iron,  converting  it  into 
soluble  protosalt. 

The  use  of  the  sulphurous  acid  fumes,  which  thus  serve  to 
supply  the  losses  of  protochlorid  of  iron,  need  not  be  resorted 
to  except  in  treating  native  carbonates  or  oxyds  of  copper,  or 
such  ores  as  contain  carbonates  of  lime  or  magnesia  or  oxyd  of 
lead  or  of  zinc,  all  of  which  cause  a  loss  of  the  protochlorid  of 
iron.  In  such  cases  the  best  mode  of  applying  the  sulphurous 
acid  is  by  using  stirring  tanks  and  passing  the  gas  over  the  sur- 
face of  the  liquid,  which  is  agitated  during  the  solution  of  the 
copper.  The  gas  should  be  as  little  diluted  with  air  as  possible. 
If  the  roasting  kiln  or  muffle  furnace  be  connected  with  the 
stirring  tank  by  an  earthenware  tube  which  enters  either  the 
cover  or  the  side  of  the  tank  at  a  point  opposite  to  that  by 
which  a  wooden  tube  (best  connected  with  a  flue)  gives  exit 
to  the  unconsumed  gas,  a  sufficiently  rapid  current  of  the  gas 
will  be  kept  up,  and  will  be  readily  absorbed  by  the  liquid  in 
the  tank. 

It  is  seldom,  however,  that  the  process  is  thus  complicated  by 
the  necessity  of  using  sulphurous  acid  gas,  for  unless  the  ob- 
jectionable matters  mentioned  above  are  present  in  considerable 
quantities  in  the  ore,  this,  if  a  sulphuret  of  copper,  will  yield 
by  careful  calcination,  as  already  explained,  enough  sulphate  of 
copper  to  compensate  for  the  loss  of  chlorid  of  iron  which  these 
would  occasion. 

By  the  introduction  of  steam  for  heating  and  of  water  for 
washing  the  residue,  the  volume  of  the  bath  becomes  slowly  aug- 
mented. To  reduce  this  it  is  therefore  necessary  to  resort  to 
evaporation,  and  for  this  purpose  it  has  been  found  that  in  the 
case  of  the  three-heated  reverberatory  furnaces  already  de- 
scribed, the  upper  hearth  may  with  advantage  be  used  for  this 
purpose.  A  shallow  basin  six  inches  deep,  of  which  the  upper 
hearth  is  the  bottom,  is  built  of  brick  lined  with  Roman  cement 


17 

prepared  as  already  described  for  brick  leaching  tanks,  with 
silicate  of  soda  and  chlorid  of  calcium.  Through  the  middle  of 
it  passes  a  funnel  or  hopper  connecting  with  the  second  hearth 
and  opening  on  the  roof  of  the  furnace  for  the  purpose  of 
charging  the  ore.  The  roof  over  the  pan  should  be  higher  than 
if  it  were  over  a  calcining  hearth,  in  order  to  give  ample  room 
to  use  a  scraper  with  which  to  remove  the  crystals  of  salt  which 
separate  during  evaporation,  and  two  doors  instead  of  three 
should  open  at  each  end  so  as  to  give  free  access  to  the  whole 
surface  of  the  pan.  Care  should  be  taken  to  keep  the  floor  of 
the  pan  free  from  accumulations  of  salt,  else  a  crust  will  be 
formed  which  is  difficult  to  remove.  When  this  arrangement  is 
used,  the  liquors  from  the  store  tank  are  run  into  the  pan  where 
they  are  exposed  to  the  escaping  current  of  hot  air  and  gases  by 
which  they  are  rapidly  evaporated,  while  at  the  same  time  they 
absorb  a  considerable  amount  of  sulphuric  acid  (which,  together 
with  sulphurous  acid,  is  formed  in  the  slow  roasting  of  pyritous 
ores),  and  thus  become  strongly  acid.  An  evaporator  of  this 
kind,  with  a  surface  of  100  square  feet,  is  easily  and  cheaply 
constructed,  is  tight  and  durable,  and  will  evaporate  a  layer  of 
four  inches  of  liquid  in  twenty-four  hours,  by  the  waste  heat. 
If  the  three  hearths  are  required  for  calcination,  large  shallow 
tanks  of  the  kind  described  may  be  constructed  between  the 
furnaces  and  the  stack,  so  that  the  whole  current  of  the  hot 
gases  shall  pass  over  the  surface  of  the  liquid,  thus  dispensing 
with  the  use  of  steam  for  heating  the  liquors  and  evaporating 
the  bath  at  the  same  time. 

IV.  Precipitating  the  Copper.  The  copper  liquors,  whether 
taken  from  the  stirring  or  settling  tanks,  or  flowing  from  the 
leaching-vats,  are  received  in  tanks  of  any  convenient  size, 
where  in  contact  with  metallic  iron  the  chlorids  of  copper  are 
decomposed,  and  the  copper  is  precipitated  in  crystalline  grains, 
plates  or  crusts,  the  texture  of  which  will  vary  according  to  the 
strength  of  liquors.  Wrought-iron  precipitates  the  copper  more 
rapidly  than  cast  iron,  but  where  this  latter  is  the  cheaper  it 
should  be  used.  If  small  scrap  is  employed  it  must  be  spread 
2 


18 

on  trays  arranged  in  the  vats.  In  the  Appendix  will  be  found 
described  a  method  of  cleaning  tinned  iron  scrap  by  which  the  tin 
may  be  saved  and  the  iron  fitted  for  precipitating  copper.  If 
the  residue  after  the  extraction  of  the  copper  is  a  nearly  pure 
oxyd-of  iron,  this  may  be  reduced  to  a  spongy  metallic  iron  by 
heating  it  for  some  hours  at  a  red  heat  with  pulverized  coal  in 
a  closed  vessel.  This  spongy  iron,  which  may  also  be  easily 
made  from  ordinary  iron  ores,  precipitates  copper  very  rapidly 
from  its  solutions,  and  is  used  for  that  purpose  in  England,  where 
it  is  prepared  in  a  reverberatory  furnace.  Details  of  the 
preparation  and  use  of  the  iron  sponge  will  be  found  in  the 
Appendix. 

From  the  precipitating  vats  the  liquor  which  has  been  de- 
prived of  its  copper,  and  in  this  .process  has  been  recharged  with 
protochlorid  of  iron,  is  drawn  off  after  twenty-four  hours  or 
more,  and  pumped  up  into  the  store  tank,  which  should  be  at  a 
higher  level  than  the  leach  vats.  It  is  then  ready  for  the 
treatment  of  fresh  portions  of  ore.  A  working  drawing  of  a 
cheap  pump  made  entirely  of  wood,  is  included  in  the  plan 
annexed. 

V.  Melting  and  Refining  the  Copper.  The  precipitating 
tanks  are  emptied  from  time  to  time,  the  cement  copper  is 
washed  with  water  and  if  small  iron  scrap  has  been  used,  is 
passed  through  a  screen  or  sieve  to  separate  any  fragments  of 
the  latter.  It  is  then  dried  at  a  gentle  heat,  when  it  is  ready 
for  refining.  In  the  treatment  of  copper  obtained  in  wet  pro- 
cesses it  is  customary  to  melt  the  cement  with  a  portion  of 
matte  or  sulphuretted  ore,  and  thus  obtain  a  crude  copper  which 
is  refined  by  a  second  fusion.  Experience  on  a  large  scale  has, 
however,  shown  that  the  purity  of  the  cement  obtained  by  the 
present  process  is  such  that  but  a  single  fusion  is  required  to 
convert  it  into  fine  copper.  The  dried,  or  even  the  moist  ce- 
ment, is  melted  down  in  a  furnace  such  as  is  used  for  refining 
blister  copper,  poled  in  the  usual  manner  and  then  cast  into 
ingots.  It  is  found  advantageous  to  mix  the  cement  with  one 
or  two  hundredths  of  coal  dust,  and  if  compressed  into  blocks 


19 

it  can  be  handled  with  greater  advantage   than  if  in  a  loose 
powder. 

VI.  Arrangement  of  Plant.  It  is  well,  when  it  can  be 
done,  to  choose  a  hill-side  as  the  site  for  works  for  carrying  out 
this  process,  so  as  to  place  the  leaching  vats  below  the  level  of 
the  calcining  furnaces.  Above  these  vats  should  be  a  water 
tank  and  also  a  store  tank  for  bath,  from  which  it  can  be  made 
to  flow  into  the  vats  placed  in  rows  on  the  lower  level.  Below 
these  should  be  placed  the  precipitating  tanks  and  still  lower  a 
large  tank  into  which  the  bath  when  deprived  of  copper  can  be 
allowed  to  flow,  and  from  which  by  means  of  the  wooden  pump 
it  is  to  be  pumped  up  into  the  store  tank  for  redistribution,  thus 
establishing  a  continuous  circulation.  Wooden  tubes  securely 
coupled  together  are  the  best  conductors  for  the  bath.  A  hor- 
izontal line  of  such  tubing  should  run  above  the  leaching  vats 
and  be  connected  with  the  store  tank  by  a  piece  of  india-rubber 
tube  or  hose,  which  can  be  closed  at  will  by  a  wooden  squeezer. 
From  this  line  of  wooden  tubing  the  bath  is  to  be  conducted  to 
each  leach  tank  by  an  india-rubber  tube,  the  flow  through 
which  is  to  be  regulated  by  squeezers.'  From  the  leach  tanks  the 
copper  liquors  should  be  conducted  through  similar  india-rubber 
tubes  into  a  covered  trough  or  launder,  running  the  whole  length 
of  the  row  of  precipitating  vats.  Such  a  trough  is  better  for 
this  purpose  than  a  closed  tube,  for  the  reason  that  when  the 
bath  is  too  cool  or  does  not  hold  a  sufficient  amount  of  salt  to 
retain  the  whole  of  the  dichlorid  of  copper  in  solution,  a  por- 
tion of  this  may  be  deposited  and  fill  up  the  tube,  while  the 
launder  can  be  watched  and  this  state  of  things  guarded  against. 

In  localities  where  a  hill-side  cannot  be  chosen  for  the  site  it 
will  be  better  to  place  both  the  leaching  and  the  precipitating 
vats  on  the  same  level  with  the  calciners,  for  it  is  easier  and 
cheaper  to  pump  the  copper  liquors  into  the  precipitating  tanks 
than  to  elevate  the  ore.  In  the  plan,  however,  for  clearness  of 
illustration  the  tanks  are  shown  on  successive  levels  in  a  build- 
ing of  three  stories. 


APPENDIX. 


I.    ASSAYING  FOR  COPPER  AND  FOR  IRON. 

The  following  directions  will  enable  any  one,  even  without  a  knowledge 
of  chemistry,  to  make  the  tests  necessary  for  the  successful  working  of  this 
process;  namely,  the  determination  of  the  quantity  of  copper  in  the  ore, 
the  character  of  the  roast,  and  the  condition  of  the  bath. 

Copper.  The  most  expeditious  and  convenient  method  for  the  determi- 
nation of  copper  depends  upon  the  property  of  cyanid  of  potassium  to  de- 
colorize the  deep-blue  solution  which  is  got  by  adding  ammonia  in  excess 
to  the  protosalts  of  copper.  Begin  by  dissolving  in  clear  water  ordinary 
commercial  cyanid  of  potassium,  in  the  proportion  of  about  a  half  a 
pound  to  a  gallon.  Next  weigh  out  carefully  five  grains  of  pure  metallic 
copper,  such  as  copper  foil ;  dissolve  it  in  a  little  nitric  acid  ;  add  water  to 
the  bulk  of  about  four  ounces,  and  then  caustic  ammonia  (liquor  ammonice^i 
until  a  deep-blue  liquid  is  obtained.  Next  fill  a  graduated  tube,  known  as 
a  burette  and  generally  divided  into  cubic  centimeters  and  fractions 
thereof,  with  the  solution  of  cyanid  of  potassium,  and  allow  this  to  drop 
from  the  burette  into  the  copper  solution,  till  the  blue  color  disappears,  first 
giving  place  to  a  pinkish  hue.  Great  care  must  be  taken  to  add  slowly 
towards  the  end  of  the  operation,  so  as  to  avoid  the  addition  of  an  excess 
of  the  cyanid.  Now  read  off  on  the  graduated  tube  the  quantity  of  the 
solution  of  cyanid  which  has  been  required  to  produce  the  decoloration  of 
the  solution  of  five  grains  of  copper.  Suppose  25.0  cubic  centimeters 
(c.c.)  have  been  consumed;  then  it  is  clear  that  one  grain  of  copper  cor- 
responds to  5  c.c.  of  the  cyanid  solution. 

To  make  an  assay  of  a  copper  ore,  reduce  it  to  fine  powder,  and  weigh 
out  carefully  25,  50,  or  100  grains,  according  as  it  is  rich  or  poor  in  copper. 
Add  to  this,  in  a  small  flask  or  beaker-glass,  common  nitric  acid,  sufficient 
in  quantity  to  cover  the  ore.  Apply  heat  to  dissolve  the  copper,  and  if  the 
ore  is  a  sulphuret  boil  it,  until,  on  adding  a  fresh  portion  of  acid,  no  more 
red  vapors  are  given  off.  Now  add  from  four  to  eight  ounces  of  water,  and 
pour  in  ammonia  till  the  blue  color  is  obtained,  and  the  liquid  shows  by  its 

(20) 


21 

smell  that  a  slight  excess  of  ammonia  has  been  added.  By  this  means  the 
dissolved  iron  (which  is  almost  always  present  in  the  ore)  will  be  separated 
as  a  bulky,  reddish-brown  peroxyd,  which  rapidly  settles,  leaving  the  clear 
blue  liquid  above.  Add  to  the  mixture  at  once  the  cyanid  of  potassium 
from  the  burette,  stirring  the  while,  and  allow  the  suspended* oxyd  of  iron 
to  settle  from  time  to  time,  so  as  to  judge  of  the  progress  of  the  operation 
from  the  color  of  the  clear  liquid,  which  soon  appears  above  the  subsiding 
precipitate  of  the  brown  peroxyd.  The  .operation  may  require  ten  or 
fifteen  minutes.  When  the  color  has  faded  out,  a«  in  the  previous  example, 
note  on  the  burette  the  quantity  of  the  cyanid  solution  consumed.  Sup- 
pose this  to  be  48  c.c.  Now  as  5  c.c.  are  equal  to  a  grain  of  copper,  we  have 
the  proportion  5  :  48  ::  1  :  9.6;  so  that,  if  the  quantity  of  ore  was  100 
grains,  the  ore  contains  9.6  p.  c.  of  copper,  or,  if  50  grains  were  employed, 
19.2  p.  c. 

In  testing  the  roasted  sulphuret  ore,  there  should  be  determined  in  each 
sample  three  things  :  (I)  the  quantity  of  sulphate  of  copper,  a  portion  of 
which,  as  already  explained,  should  always  be  present ;  (2)  the  amount  of 
oxyd  of  copper ;  and  (3)  the  quantity  of  unoxydized  copper,  existing  in 
the  form  of  sulphuret.  As  sulphate  of  copper  is  readily  soluble  in  water, 
it  is  only  necessary  for  the  first  determination  to  boil  a  weighed  portion  of 
the  ore  with  a  little  water,  pour  off  the  clear  solution,  wash  the  residue 
with  cold  water,  add  ammonia  to  the  liquid,  and  proceed  as  before.  Muri- 
atic acid  diluted  with  twenty-five  times  its  bulk  of  water  will,  at  a  boiling 
heat,  readily  dissolve  the  oxyd  of  copper  from  the  roasted  ore,  without  at- 
tacking the  sulphuret.  If  then  we  boil  the  roast  for  two  or  three  minutes 
with  a  sufficient  quantity  of  such  dilute  acid,  allow  the  undissolved  portion 
to  settle,  and  wash  it  thoroughly  with  several  waters,  the  only  copper  left 
in  the  residuewill  be  that  of  the  sulphuret  which  has  escaped  roasting 
and  which  may  be  dissolved  by  boiling  with  nitric  acid. 

Suppose  100  grains  of  a  roasted  ore  to  be  boiled  with  water:  the  clear 
solution  is  poured  off,  mixed  with  ammonia,  and  treated  with  the  standard 
solution  of  cyanid  of  potassium,  of  which  15  c.c.  are  consumed.  Then 
5  :  15  ::  1  :  3  ;  so  that  the  sample  holds  3.0  p.  c.  of  copper  as  soluble  sulphate. 
The  residue  is  now  boiled  for  two  or  three  minutes  with  two  ounces  or  more 
of  dilute  muriatic  acid,  as  already  described,  and  the  solution  then  obtained 
decanted  and  boiled  for  a  minute  with  a  few  drops  of  nitric  acid,  to  convert 
any  dichlorid  into  protochlorid  of  copper  (this  is  necessary  to  get  the  full 
color,  because  the  ammoniacal  solution  of  the  dichlorid  is  colorless) .  Am- 
monia is  now  added,  and  then  the  standard  cyanid  solution.  If  of  this  32 
c.c.  are  required  to  decolorize,  we  have  5  :  32  ::  1  :  6.4,  or  6.4  p.  c.  of  cop- 
per in  the  state  of  soluble  oxyd.  The  insoluble  residue  is  then  boiled  with 
nitric  acid  till  red  fumes  are  no  longer  given  off,  which  may  take  as  much 


22 

as  five  or  ten  minutes,  water  is  added,  and  excess  of  ammonia,  when  it  is 
found  that  2  c.c.  of  the  standard  solution  of  cyanid  are  required  for  decol- 
orizing. We  have  thus  5  :  2  ::  1  :  0.4;  so  that  there  remained  0.4  p.c.  of 
copper  as  insoluble  sulphuret.  The  result  will  then  stand  as  follows  :  — 

Copper  as  sulphate 3.0 

"       "  oxyd 6.4 

"       "  sulphid 0.4 

9.8 

In  thus  assaying  a  sample  of  ore,  the  percentage  of  copper  in  which  is 
known,  we  may  dispense  with  directly  determing  the  oxyd,  and  by 
deducting  from  the  total  the  amount  of  soluble  sulphate  and  insoluble  sul- 
phuret, we  find  the  quantity  of  oxyd  by  loss.  In  the  regular  working  of  the 
process,  in  fact,  it  is  only  necessary  to  determine  the  sulphate  and  the 
sulphuret  of  the  roast.  The  former  is  important,  because  as  already  ex- 
plained, it  is  necessary  to  have  a  certain  portion  of  sulphate  to  make  up  for 
the  loss  of  protochlorid  of  iron  in  the  bath,  and  the  second  because  the 
copper  which  remains  unroasted  in  the  form  of  insoluble  sulphuret  is  not 
extracted  by  the  bath,  and  therefore  is  lost. 

The  above  process  of  copper  assaying,  though  the  most  simple  and  ex- 
peditious, is  not  directly  applicable  to  ores  containing  silver,  zinc,  cobalt, 
nickel  or  manganese.  The  absence  of  the  first  may  always  be  ensured  by 
adding  a  few  drops  of  muriatic  acid  to  the  solution,  by  which  silver  is 
thrown  down  as  a  white  insoluble  chlorid.  When,  as  is  not  infrequently 
the  case,  one  or  more  of  the  other  metals  mentioned  are  present,  the  fol- 
lowing modification  of  the  process  may  be  adopted.  The  solution  from  tha 
roasted  ore  by  water,  mixed  with  a  little  muriatic  acid,  or  the  solution  of 
the  oxyd  of  copper  in  this  acid,  is  digested  with  metallic  iron  or  zinc,  by 
which  the  whole  of  copper  is  thrown  down  in  a  spongy  metallic  form,  while 
the  metals  zinc,  cobalt,  nickel  and  manganese,  which  would  vitiate  the 
operation  of  decoloration,  remain  dissolved.  Iron  wire  or  a  slip  of  sheet 
zinc  may  be  used,  and  if  heat  be  applied  the  precipitation  of  the  copper 
will  generally  be  finished  in  half  an  hour.  It  may  be  known  to  be  complete 
when  a  bit  of  clean  bright  iron  dipped  for  a  minute  in  the  liquid  gets  no 
color  of  copper  upon  its  surface.  The  metallic  copper  precipitated  is  care- 
fully separated  from  the  iron  or  zinc,  washed  with  water,  dissolved  in  a 
little  nitric  acid,  mixed  with  an  excess  of  ammonia  and  determined  by  the 
use  of  a  cyanid  solution  as  before. 

When  a  copper  ore  has  been  dissolved  by  nitric  acid  it  is  necessary  to  get 
rid  of  this  acid  before  precipitating  the  copper.  To  this  end  the  nitric 
solution  is  to  be  evaporated  nearly  to  dry  ness,  then  mixed  with  about  as 
much  muriatic  acid  as  had  been  used  of  nitric*  and  again  evaporated  nearly 
to  dryness.  Water  is  now  added,  and  from  the  solution  the  metallic  cop 


23 

per  precipitated  by  iron  or  by  zinc,  and  determined  in  the  manner  already 
described.  The  amount  of  copper  held  in  solution  at  any  time  by  the  bath, 
is  also  readily  determined  by  precipitation  with  iron  or  zinc.  It  is  well  to 
add  thereto  a  few  drops  of  muriatic  acid,  and  heat  quickens  the  process.  If 
the  quantity  of  copper  precipitated  is  considerable,  we  may  conveniently 
wash  it  with  water  several  times,  then  with  a  little  alcohol,  dry  it  at  a  gentle 
heat  and  weigh  it  directly.  Smaller  quantities  are  however  best  determined 
by  dissolving  the  precipitated  copper  in  nitric  acid,  adding  ammonia  and 
the  standard  solution  of  cyanid. 

The  cyanid  solution  is  liable  to  slow  decomposition,  by  which  its  strength 
is  diminished,  so  that  from  time  to  time  the  stock  of  the  solution  (which 
should  be  kept  in  well-stoppered  bottles  and  out  of  the  direct  light,),  must 
be  standardized  afresh  by  a  solution  of  a  known  quantity  of  copper  as 
already  explained.  If  the  solution  becomes  turbid  it  may  be  filtered 
through  paper. 

Iron.  The  following  simple  and  rapid  mode  of  assaying  for  iron  in  the 
bath,  is  based  upon  the  fact  that  the  deep  crimson  color  of  a  solution  of 
permanganate  of  potash  (mineral  chameleon)  is  at  once  destroyed  by  a 
protosalt  of  iron,  such  as  protosulphate  or  protochlorid.  It  is  therefore 
only  necessary  to  add  to  the  acid  and  dilute  solution  of  a  protosalt  of  iron, 
which  is  colorless,  a  solution  of  the  crimson  permanganate  of  known 
strength  until  the  tint  of  the  latter  remains  in  the  liquid.  We  begin  by  dis- 
solving five  grains  of  pure  clean  iron  wire  (like  that  used  for  piano  strings)  in 
dilute  sulphuric  or  muriatic  acid,  and  then  add  half  a  pint  or  more  of  pure 
cold  water,  and  a  few  drops  of  sulphuric  acid.  Now  pour  from  a  tube  or 
burette  graduated  like  that  used  for  the  cyanid  solution  in  copper  testing,  a 
dilute  solution  of  the  permanganate,  rapidly  at  first,  and  then  more  slowly 
constantly  stirring,  till  the  iron  solution  acquires  a  faint  crimson  tint.  The 
quantity  of  chameleon  solution  employed,  divided  by  the  number  of  grains 
of  iron,  will  give  the  number  of  cubic  centimeters  which  correspond  t3  a 
grain  of  this  metal.  As  the  bath  used  in  the  Hunt  and  Douglas  process 
contains  the  iron  in  the  state  of  protochlorid  it  is  only  necessary  to  take  a 
known  volume  of  it  and  proceed  as  above  to  determine  its  content  of  iron. 
If,  for  example,  the  permanganate  solution  is  of  such  a  strength  that  a 
solution  of  five  grains  of  iron  requires  42  cubic  centimeters  of  chameleon 
solution  to  color  it,  equal  to  8.4  c.c.  for  a  grain  of  iron,  we  take  two  fluid 
drachms  (a  quarter  of  a  fluid  ounce)  of  the  bath,  add  thereto  twenty  drops  of 
sulphuric  acid  and  half  a  pint  of  pure  cold  water  and  find  that  it  requires 
12.6  c.c.  of  chameleon  to  give  it  a  crimson  tint,  then  8.4  :  12.6  ::  1.0  :  1.5 
so  that  this  quantity  of  the  bath  contains  1.5  grains  of  metallic  iron,  equal 
to  6  grains  to  the  fluid  ounce.  By  testing  in  this  manner  from  day  to  day 
a  measured  quantity  of  the  bath,  its  loss  or  gain  in  iron  can  be  very  easily 
determined. 


24 

The  solution  of  the  permanganate  should  be  kept  in  a  glass-stoppered 
bottle  and  should  be  tested  from  time  to  time  with  a  solution  containing  a 
known  weight  of  iron.  For  this  purpose,  instead  of  iron  wire,  which  re- 
quires some  time  to  dissolve  in  acid,  we  may  conveniently  use  the  double 
sulphate  of  protoxyd  of  iron  and  ammonia  (ammonio-ferrous  sulphate). 
The  green  readily  soluble  crystals  of  this  salt  contain  exactly  one-seventh 
their  weight  of  iron,  so  that  35  grains  of  this  salt,  with  20  drops  of  sulphuric 
acid  dissolved  in  half  a  pint  of  water,  correspond  to  a  solution  of  5  grains  of 
metallic  iron. 

n.  PREPARATION  AND  USE  OF  IRON  SPONGE. 

The  use  of  spongy  metallic  iron  for  precipitating  copper  in  a  metallic 
condition  from  its  solutions  was  proposed  in  1859  by  Mr.  William 
Gossage,  of  Widnes,  England,  to  whom  letters  patent  for  improve- 
ments in  extracting  copper  were  then  granted  in  Great  Britain,  the 
dates  of  the  specification  being  March  7  and  September  7  of  that  year 
(patent  No.  194).  He  claimed  the  extraction  of  copper  from  the  residues 
of  calcined  pyrites  by  the  use  of  solutions  of  persalts  of  iron.  The  copper 
thus  dissolved  being  thrown  down  by  metallic  iron,  he  obtained  a  protosalt 
of  iron  (protosulphate  or  protochlorid),  which  he  converted  by  evaporation 
and  exposure  to  the  air  at  a  heat  below  redness  into  a  mixture  of  insoluble 
peroxyd  and  of  a  persalt  soluble  in  water,  which  could  be  used  to  dissolve 
another  portion  of  copper.  In  the  case  of  silver-bearing  ores  he  combined 
the  persalt  of  iron  with  common  salt,  to  dissolve  the  chlorid  of  silver  formed. 

In  the  same  patent  he  claimed  for  the  precipitation  of  the  dissolved  cop- 
per finely  divided  or  spongy  iron  prepared  from  calcined  pyrites  residues 
containing  a  portion  of  copper,  '*  by  mixing  them  with  about  one-fourth 
their  weight  of  coal,  coke,  or  charcoal,  in  coarse  powder,  and  introducing  the 
mixture  into  an  oven  or  closed  furnace  kept  at  a  red  heat  for  about  twelve 
hours,  or  until  the  greater  part  of  the  oxyd  of  iron  contained  therein  has 
become  converted  into  metallic  iron.  I  then  withdraw  the  product  as  quickly 
as  possible,  and  I  receive  it  either  in  vessels  containing  water,  or  in  vessels 
from  which  the  air  can  be  excluded  till  the  contents  have  become  sufficiently 
cooled."  "  I  employ  metallic  iron  obtained  by  the  means  herein  described 
for  the  precipitation  of  copper  from  its  solutions,  in  the  same  manner  that 
other  metallic  iron  is  employed  for  effecting  such  precipitation."  In  1862 
Gustav  Bischof,  Jr.,  obtained  letters  patent  in  Great  Britain  for  the  man- 
ufacture of  spongy  iron  for  precipitating  copper,  the  materials  used  and 
the  mode  of  working  being  essentially  the  same  as  those  of  the  earlier 
patent  of  Gossage,  and  in  1868  a  United  States  patent  for  the  same  inven- 
tion was  granted  Mr.  Bischof  and  his  assignee  Mr.  John  S.  Kidwell. 


25 

The  manufacture  of  iron  sponge  for  this  purpose  as  carried  on  at  New- 
castle, in  England,  is  described  in  a  paper  read  before  the  Newcastle 
Chemical  Society  by  Mr.  Gibbs,  and  published  in  Engineering  and  in  Van 
Nostrand's  Engineering  Magazine  for  October,  1875,  from  which  the  fol- 
lowing notes  and  extracts  are  made : 

The  ore  now  treated  for  copper  by  wet  process  in  England  is  the  residue 
of  the  Spanish  pyrites  (of  which  nearly  400,000  tons  are  there  annually 
consumed),  which  has  been  calcined  to  extract  its  sulphur,  and  is  then  known 
as  burnt  ore.  It  contains  3  or  4  p.  c.  of  copper,  as  much  sulphur,  a  little 
arsenic,  lead,  and  zinc,  and  about  2  p.  c.  of  silicious  matter.  By  calcination 
with  about  15  p.  c.  of  salt,  in  what  is  known  as  the  Longmaid  or  Henderson 
process  and  washing  with  water  and  with  dilute  muriatic  acid,  the  copper, 
sulphur  and  arsenic  are  removed,  and  the  residue,  known  as  purple  ore,  is 
nearly  pure  peroxyd  of  iron.  Both  Gossage  and  Bischof  proposed  the  use 
of  the  burnt  ore  for  the  manufacture  of  the  sponge  on  the  ground  that  the 
copper  present  would  be  obtained  with  the  precipitate;  but  the  arsenic 
which  remains  in  the  burnt  ore  is  such  an  objectionable  impurity  that,  ac- 
cording to  Mr.  Gibbs,  only  the  purified  or  purple  ore  is  now  employed  for 
the  manufacture  of  sponge  for  copper  precipitation.  He  thus  describes  the 
furnace  and  its  working: 

"  This  is  essentially  a  reverberatory  furnace,  30  ft.  long,  with  a  provision 
for  conveying  the  flame  under  the  hearth,  after  it  has  passed  over  the 
charge.  The  hearth  of  the  furnace  is  23  ft.  long  and  8  ft.  wide,  and  is 
divided  into  three  working-beds  by  bridges.  Each  bed  has  two  working- 
doors  on  one  side.  The  doors  slide  in  grooves,  and  close  air-tight.  The 
fire-box  is  4  ft.  by  3  ft. ,  with  bars  4  ft.  8  in.  below  the  bridge,  thus  allow- 
ing for  a  considerable  depth  of  burning  fuel.  The  fire-door  slides  in 
grooves  like  the  working-doors.  The  hearth  is  formed  of  tiles  sustained 
on  brickwork  partitions,  forming  flues  through  which  the  flame  returns  after 
passing  over  the  hearth.  From  these  flues  the  flame  drops  by  a  vertical 
flue  alongside  the  fire-bridge,  to  an  underground  flue  communicating  with  a 
chimney.  The  entrance  to  the  latter  flue  is  provided  with  a  fire-tile  dam- 
per, which  is  closed  whenever  the  working  or  fire-doors  of  the  furnace  have 
to  be  opened.  A  cast-iron  pan,  20  ft.  by  10  ft.,  is  carried  by  short  columns 
and  girders  over  the  furnace-roof.  In  this  pan  the  ore  is  dried  and  mixed 
with  coal,  and  from  it  is  charged  into  the  hearth  through  cast-iron  pipes  » 
built  into  the  furnace-arch.  The  furnace  is  elevated  on  brick  pillars,  to 
allow  of  iron  cases  running  under  it,  and  it  is  worked  from  a  platform  of 
cast-iron  plates.  A  vertical  pipe,  6  in.  diameter,  passes  through  the  hearth 
of  the  furnace,  inside  each  working-door;  and  through  these  pipes  the  re- 
duced iron  is  discharged  into  iron  cases  placed  beneath.  These  cases  are 
horizontally  rectangular,  and  taper  upwards  on  all  sides.  The  cover  is 
3 


26  • 

fixed,  and  in  its  centre  is  a  hole  6  in.  diameter,  with  a  flange  upwards 
which  serves  to  connect  the  case  with  the  discharging-pipe.  The  bottom  of 
the  case  is  closed  by  a  folding-door,  hinged  on  one  side,  and  secured  by 
bolts  and  cutters  on  the  other.  The  case  is  fitted  with  four  wheels,  clear 
of  the  door,  and  is  covered  with  a  cast-iron  plate,  fitting  loosely  into  the 
opening  on  the  upper  side.  It  stands  4  ft.  8.  in.  high,  and  has  a  capacity 
of  12  cubic  feet." 

"  The  furnace-hearth  being  at  a  bright  red  heat,  each  of  the  three  work- 
ing-beds is  charged  with  20  cwt.  of  dry  purple  ore,  and  6  cwt.  ground  coal 
from  the  cast-iron  pan  under  the  roof.  The  fire  and  working  doors  are 
closed,  and  the  only  air  entering  is  that  through  the  fire,  in  working  which 
care  is  taken  to  prevent  the  mass  of  burning  fuel  getting  hollow.  The 
charge  in  the  first  bed  from  the  fire-bridge  is  reduced  in  from  nine  to  twelve 
hours;  in  the  second,  in  eighteen  hours;  and  in  the  third,  in  about  twenty- 
four  hours.  Each  charge  is  stirred  over  two  or  three  times  during  the 
period  of  reduction.  Before  opening  any  door  the  flue-damper  is  closed,  to 
prevent  a  current  of  air  entering  over  the  charge.  On  the  complete  reduc- 
tion of  the  charge  on  any  working-bed,  two  cases  are  run  under  the  bottom 
pipe,  to  which  their  mouths  are  luted  by  clay,  and  the  charge  is  quickly 
drawn  into  them,  by  rakes  worked  through  the  doors.  The  cases  are  then 
closed  with  cast-iron  plates.  In  about  forty-eight  hours  the  iron  is  cooled 
sufficiently  to  be  discharged ;  and  this  is  simply  done  by  raising  the  case  by 
a  crane,  and  knocking  out  the  cutters  fastening  the  hinged  door  on  the 
bottom,  when,  from  the  tapering  form  of  the  case,  the  mass  of  reduced  iron 
falls  out  readily.  The  sponge  is  ground  to  powder  under  a  pair  of  heavy 
edge-stones,  6  ft.  in  diameter,  and  is  passed  through  a  sieve  of  fifty  holes 
per  linear  inch. " 

The  heat  being  a  bright  red,  the  reduction  of  the  charges  is  sure  to  take 
place  on  the  hearths  in  the  times  specified ;  but  it  may  be  completely  though 
more  slowly  effected  at  a  very  dull  red.  The  material  used  is  said  to  con- 
tain 95  p.  c.  of  peroxyd  of  iron  ;  and  the  product  holds  metallic  iron  70.40, 
peroxyd  8.15,  protoxyd  2.40,  sulphur  1.07,  copper  0.24,  with  small  portions 
of  lead  and  zinc,  7,60  of  carbon,  and  9.80  of  silicious  residue;  so  that 
about  90  p.  c.  of  the  iron  of  the  charge  is  reduced  to  the  metallic  state. 
If  we  suppose  that  four  charges  of  20  cwt.  each  of  such  ore  are  reduced  in 
twenty-four  hours,  the  yield  would  be  nearly  48  cwt.  of  metallic  iron. 

"  In  using  spongy  iron  in  precipitating  copper,  the  liquids  are  agitated  by 
an  air-blast  while  the  iron  is  gradually  added.  By  this  means  a  very  per- 
fect mixture  is  obtained,  and  a  copper  precipitate  can  be  readily  produced, 
containing  not  more  than  1  p.  c.  of  metallic  iron.  As  compared  with  pre- 
cipitation by  scrap  iron,  the  economy  of  space  required  and  facility  of  ma- 
nipulation are  very  great.  On  the  side  of  spongy-iron  precipitation  are 


27 

cheapness  of  material  and  economy  of  application;  while  against  it  is  the 
presence  with  the  precipitated  copper  of  the  unreduced  iron  oxides  and 
excess  of  carbon  from  the  reduction.  In  employing  spongy  iron,  the 
copper-extractor  has  the  production  of  the  precipitant  in  his  own  hands, 
and  avoids  the  troublesome  handling  of  a  material  so  cumbrous  as  scrap 
iron." 

It  is  comparatively  rare  that  the  residue  from  copper  ores  treated  in  the 
wet  way,  will  yield  an  oxyd  of  iron  approaching  in  purity  to  that  obtained 
from  Spanish  pyrites;  and  it  is  clear  that  an  oxyd  containing  a  large  pro- 
portion of  earthy  matter  is  not  fitted  for  the  production  of  iron  sponge  for 
copper  precipitation,  inasmuch  as  the  whole  of  this  would  remain  as  an 
impurity  in  the  cement  copper.  The  purer  native  oxyds  of  iron,  however, 
such  as  the  magnetic  and  specular  ores,  may  be  advantageously  employed 
for  the  production  of  sponge,  by  grinding  them  to  powder  and  heating 
with  an  admixture  of  coal,  as  already  described. 

The  production  of  pure  spongy  iron,  on  a  commercial  scale,  has  lately 
been  perfected  by  Mr.  T.  S.  Blair,  of  Pittsburg,  by  means  of  an  ingenious 
gas-furnace  in  which  the  ore  in  small  masses  is  heated  to  redness  with 
coarsely  powdered  charcoal.  The  iron  thus  prepared,  being  free  from  oxyd 
and  from  the  earthy  matters  of  the  fuel,  is  fitted  for  the  manufacture  of  fine 
steel;  but  this  perfected  process  is  not  adapted  to  powdered  ores  and 
residues  like  those  from  pyrites.  As  a  matter  of  economy  it  remains  to  be 
seen  whether  the  somewhat  impure  iron  sponge,  which  may  be  very  econon- 
ically  prepared  from  these,  is  to  be  preferred  to  the  purer  sponge,  which  is 
made  on  a  large  scale  and  cheaply  in  Mr.  Blair's  furnaces. 


III.    USE  OF  TIN  PLATE  SCRAP. 

Tin  plate,  which  is  iron  coated  with  tin,  may  be  advantageously  used  for 
precipitating  copper,  when,  as  in  the  Hunt  and  Douglas  process,  the  so- 
lutions contain  protochlorid  of  copper,  together  with  a  soluble  sulphate, 
as  sulphate  of  soda.  A  heated  solution  of  this  kind  very  readily  removes 
the  tin  from  the  iron,  and  causes  its  separation  in  white  flakes  of  insoluble 
hydrated  peroxyd  of  tin,  with  the  liberation  of  a  portion  of  free  hydrochloric 
acid,1  leaving  the  iron  in  a  state  fit  for  the  precipitation  of  the  copper.  In 
practice  the  tin  plate  scrap  may  be  used  directly  in  the  vats  in  place  of 

1  In  this  reaction  protochlorid  of  copper  and  metallic  tin  yield  dichlorid  of  copper  and 
perchlorid  of  tin,  which  last,  in  solution  and  in  the  presence  of  a  sulphate,  is  broken  up 
into  hydrated  peroxyd  of  tin  and  free  hydrochloric  acid.  The  final  result  of  the  reaction 
may  be  thus  represented : 

4CuCl  +  Sn  +  H2O2  =  2Cu2Cl  +  SnO3  +  2HC1. 


28 

scrap  iron,  in  which  case  the  tin  oxyd  remains  mixed  with  the  cement 
copper,  and  will  be  more  or  less  completely  washed  away  in  the  subsequent 
stages  of  the  process.  Otherwise  the  tin  plate  scrap  may,  by  a  simple  ar- 
rangement, be  immersed  for  a  few  minutes  in  the  hot  copper  solution  till 
the  tin  is  taken  off,  and  may  then  be  removed  to  the  copper-precipitation 
tanks.  The  separated  tin  oxyd  may  be  collected  by  subsidence,  freed  from 
any  adhering  metallic  copper  by  washing  with  a  portion  of  the  hot  solu- 
tion containing  protochlorid  of  copper,  and  when  thus  purified  reduced  to 
the  metallic  state  or  used  for  the  manufacture  of  stannate  of  soda.  Ordi- 
nary tin  plate  carries  3  or  4  p.  c.  of  tin. 

As  tin  plate  scrap  has,  in  most  places,  little  or  no  commercial  value,  it 
may  often  be  advantageously  employed  for  the  precipitation  of  copper  from 
its  solutions.  The  process  above  described  was  made  the  subject  of  letters 
patent  granted  to  Thomas  Sterry  Hunt,  May  19,  1874,  (No.  150,957)  for 
"  An  improvement  in  precipitating  copper  by  means  of  tin  scrap,"  the 
claim  being  as  follows: 

1.  "  The  use  and  application  of  tin  plate  scrap  or  waste  for  precipita- 
ting copper  from  its  solutions,  substantially  as  above  described." 

2.  "  The  recovery  and  utilization  of  the  tin  from  the  tin  plate  scrap  by 
means  of  its  solution  and  subsequent  precipitation  as  oxyd  of  tin  in  solu- 
tions containing  protochlorid   of  copper  and  a  sulphate,  substantially  as 
above  described." 


IV.     CHEMISTRY  OF  THE  HUNT  AND  DOUGLAS  PROCESS. 

The  peculiarity  of  this  method  is  the  use  of  a  solution  of  protochlorid 
of  iron  and  chlorid  of  sodium  to  render  soluble  the  oxydized  com- 
pounds of  copper.  In  the  wet  process  now  generally  adopted  in  Great 
Britain  and  mentioned  on  page  25,  where  the  ores  are  calcined  with  com- 
mon salt,  this  is  in  great  part  decomposed  with  the  formation  of  sulphate  of 
soda  and  chlorids  of  copper,  which  are,  in  their  turn,  decomposed  when  in 
solution,  by  contact  with  iron,  with  separation  of  metallic  copper  and 
production  of  protochlorid  of  iron.1 

1  The  concentrated  liquid  obtained  by  leaching  the  ores  in  this  process  at  Widnes  in  Eng- 
land gave,  according  to  Claudet,  for  a  litre  of  specific  gravity  1.24;  sulphate  of  soda  14.41 
grammes ;  chlorid  of  sodium  6.39 ;  chlorids  of  copper  and  other  metals  12.75,  containing 
chlorine  6.61,  copper  5.28,  zinc  0.68,  lead  0.057,  iron  0.045,  silver  0.004,  besides  a  little  gold 
and  small  but  undetermined  quantities  of  arsenic,  antimony  and  bismuth.  Of  the  copper 
0.580  was  in  the  state  of  dichlorid.  The  silver  extracted  from  this  solution  by  Claudet's 
method,  with  iodine,  contains  about  1.3  p.  c.  of  gold.  Chemical  News,  Vol.  xxn,  p.  184. 


29 

The  liquid  thus  obtained,  holding  an  abundance  of  protochlorid  of  iron 
with  a  little  chlorid  of  sodium,  is  found  to  have  but  a  feeble  solvent  action 
upon  the  oxyd  of  copper  and  is  accordingly  thrown  away,  polluting  the 
rivers,  and  thus  giving  rise  to  serious  difficulties  in  England.  Various  at- 
tempts have  been  made  to  utilize  the  chlorid  of  iron  in  these  waste  liquors 
for  chloridizing  copper.  Gossage  patented  a  plan  which  consisted  in  evap- 
orating them  to  dryness  and  heating  the  residue  in  contact  with  air  to  low 
redness,  by  which  means  there  is  obtained  a  mixture  of  insoluble  peroxyd 
and  soluble  perchlorid  of  iron  (see  page  24).  Henderson  effects  the  same 
result  by  the  action  of  air  on  the  liquors  at  ordinary  temperatures.  He 
also  by  decomposing  the  evaporated  waste  liquors  at  a  strong  red  heat  in 
contact  with  silicious  matters,  gets  perchlorid  of  iron  in  vapor  with  some 
hydrochloric  acid  and  free  chlorine,  and  dissolves  these  in  a  solution  of 
protochlorid  of  iron,  thus  getting  a  solution  of  perchlorid  of  iron,  the  sol- 
vent action  of  which  on  oxyd  of  copper  is  well  known.  (British  patent  of 
May,  1865,  No.  1255,  and  United  States  patent,  Dec.,  1866,  No.  60,514.) 

To  dispense  with  these  tedious  and  costly  processes  and  enable  liquor, 
containing  protochlorid  of  iron  to  be  directly  used  for  the  solution  of  copper, 
was  much  to  be  desired.  It  was  found  that  when  a  solution  of  protochlorid 
of  iron  is  brought  in  contact  with  either  protoxyd  or  dinoxyd  of  copper, 
dichlorid  of  copper  is  formed,  which,  being  insoluble  in  water,  soon  coats 
over  the  oxyd  and  arrests  the  chloridizing  process.  To  overcome  this  diffi- 
culty, however,  it  was  only  necessary  to  add  a  hot  and  strong  solution  of 
common  salt  in  which  (as  in  all  other  solutions  of  chlorids)  the  dichlorid  of 
copper  has  a  considerable  degree  of  solubility.  The  reactions  of  the  two 
oxyds  of  copper  with  protochlorid  of  iron  are  unlike.  Three  equivalents  of 
the  protoxyd,  containing  95.25  of  copper,  when  brought  in  contact  with  an 
excess  of  solution  of  the  protochlorid  under  the  conditions  just  explained, 
react  with  two  equivalents  of  it,  containing  56.00  of  iron,  and  yield  one 
equivalent  of  the  protochlorid  of  copper,  which  is  readily  soluble  in  water, 
and  contains  31.75  of  copper,  and  35.50  of  chlorine,  and  one  equivalent  of 
the  insoluble  dichlorid,  in  which  the  same  amount  of  chlorine  is  united  with 
twice  as  much,  or  63.50  of  copper.  When  the  copper  is  in  the  state  of  the 
dinoxyd,  only  one-half  as  much  protochlorid  of  iron  is  consumed,  and  there 
is  formed  for  the  same  amount  of  dichlorid  as  before,  one  equivalent,  or 
31.75  of  metallic  copper.  This  would  remain  undissolved  if  the  dinoxyd 
alone  were  treated,  but  metallic  copper  in  presence  of  an  excess  of  proto- 
chlorid of  copper  is  at  once  converted  into  the  dichlorid,  so  that  if  one-half 
of  the  oxydized  copper  in  a  mixture  treated  with  an  excess  of  protochlorid 
of  iron,  is  protoxyd  and  one-half  dinoxyd,  the  whole  of  the  copper  passes 


30 

into  the  state  of  dichlorid.1  For  this  reason  it  is  necessary,  in  submitting 
dinoxyd  ores  to  this  process,  either  to  mix  them  with  a  sufficient  amount  of 
ores  containing  protoxyd,  or  to  calcine  them  slightly  in  the  air,  so  as  to  con- 
vert one-half  or  more  of  the  dinoxyd  into  protoxyd  of  copper. 

In  the  reaction  between  the  oxyd  of  copper  and  protochlorid  of  iron,  the 
iron  of  the  latter  separates  from  the  solution  as  a  reddish  brown  insoluble 
precipitate  of  hydrous  peroxyd,  which  carries  with  it  a  small  portion  of 
chlorine  in  the  form  of  an  oxychlorid  of  iron,  due  to  secondary  reactions 
and  in  part  to  the  action  of  the  air  upon  the  solution  of  protochlorid  of 
iron.  The  amount  of  chlorine  thus  removed,  and  consequently  lost  to  the 
bath,  was  found,  in  carefully  conducted  experiments,  to  vary  from  5  to  10 
.p.  c.  of  that  originally  united  with  the  iron,  that  is  to  say  for  100  parts  of 
protochlorid  of  iron  consumed  in  chloridizing  copper,  the  regenerated  bath 
will  contain  from  90  to  95  parts.  This  loss  of  chlorine  must  in  all  cases  be 
supplied  if  the  strength  of  the  bath  is  to  be  kept  up,  an  end  which  is  readily 
obtained  in  one  or  two  ways.  When  sulphuretted  ores  are  oxydized,  there 
is  always  formed  a  portion  of  sulphate  of  copper,  which,  with  careful  roasting 
(page  10),  may  equal  one-fourth  or  even  one-half  of  the  copper  present. 
This  sulphate  when  decomposed  by  metallic  iron  gives  protosulphate  of 
iron,  which,  by  its  reaction  with  salt  yields,  as  we  have  seen  in  the  prepar- 
ation of  the  bath,  sulphate  of  soda  and  protochlorid  of  iron,  which  in 
ordinary  cases  more  than  suffices  to  supply  any  loss  of  chlorine.  If,  as 
sometimes  happens,  there  is  found  too  large  a  portion  of  .these  compounds, 
this  may  be  corrected  by  adding  to  the  bath,  previously  freed  from  copper, 
a  small  quantity  of  slaked  lime,  by  which  means  the  excess  of  sulphate  and 
of  iron  are  precipitated  in  the  form  of  sulphate  of  lime  and  protoxyd  of 
iron,  from  which  the  clear  liquid  may  be  drawn  or  filtered  off. 

The  bath  made,  as  already  described,  with  280  pounds  of  copperas  (equal 
to  56  pounds  of  iron)  and  320  pounds  of  salt  in  2000  pounds  of  water,  has 
a  specific  gravity  of  about  22°  Beaume  or  1.150  at  ordinary  temperatures, 
water  being  1.000.  A  cubic  foot  of  it  weighs  1150  ounces  avoirdupois  and 
contains  3.52  Ibs.  of  protochlorid  of  iron  (besides  an  equal  quantity  of 
sulphate  of  soda),  and  about  5^  Ibs.  of  salt.  This  amount  of  protochlorid 
contains  1.54  Ibs.,  or  10,780  grains  of  metallic  iron,  and  as  a  cubic  foot  is 

1The  reactions  between  protochlorid  of  iron  and  the  oxyds  of  copper  are  thus  expressed 
in  chemical  symbols,  using,  as  has  been  done  in  the  note  on  page  27,  the  older  notation,  in 
which  Cu  =  31.75,  Fe  =  28,  Cl =  35.6,  and  O  =  8. 
For  the  protoxyd  of  copper. 

3Cu2O2  +  4FeCl  =  2Fe2O3  +  2CuaCl  +  2CuCl. 
For  the  dinoxyd  of  copper, 

3Cu2O  +  2FeCl  =  Fe2O3  +  2Cu2Cl  +  2Cu. 

In  the  reaction  between  the  protochlorid  of  copper  and  the  metallic  copper, 
2CuCl  +  2Cu  =  2Cu2Cl. 


31 

equal  to  almost  exactly  1000  fluid-ounces,  each  fluid-ounce  holds  in  solution 
10.78  grains  of  iron  as  protochlorid.  By  the  method  of  assay  described 
above,  the  amount  of  iron  held  in  solution  by  a  fluid-ounce  of  the  liquid 
is  very  easily  determined,  and  in  this  way  the  efficiency  of  a  bath  is  most 
conveniently  designated.  Solutions  containing  5.0  grains,  and  even  3.0 
grains  of  dissolved  iron  to  the  fluid-ounce,  may  be  used,  but  the  strongest 
are  most  efficient 

The  protochlorid  of  iron  serves  to  chloridize  the  oxyd  of  copper  in  the 
ore.  A  cubic  foot  of  bath  containing  10,780  grains  of  dissolved  iron  will 
chloridize  18,287  grains  (or  2.61  Ibs.)  of  copper  in  the  state  of  protoxyd, 
converting  one-third  of  it  into  protochlorid,  and  two-thirds  of  it  into  di- 
chlorid  of  copper,  of  which  latter 'compound  (consisting  of  copper  63.5, 
chlorine  35.5)  there  will  be  formed  29,057  grains,  or  about  4.15  Ibs.  The 
dichlorid  is  insoluble  in  water  though  readily  soluble  in  strong  brine,  espe- 
cially if  this  be  heated;  hence  the  necessity  of  a  large  excess  of  salfin  the 
bath.  A  cubic  foot  of  saturated  brine  at  a  temperature  of  194°  F.  will 
dissolve  about  10.0  Ibs.,  and  at  104°  F.  about  5.0  Ibs.  of  the  dichlorid, 
while  a  cubic  foot  of  brine  holding  15  p.  c.  of  salt,  will  dissolve  at  194°  F. 
6.25  Ibs.,  at  184°  F.  3.75  Ibs.,  and  at  57°  F.  2.18  Ibs.  of  dichlorid  of  copper, 
and  the  same  amount  of  brine  holding  only  5  p.  c.  of  salt  will  dissolve  at 
198°  1.65  Ibs.,  and  at  104°  0.70  Ibs.  of  dichlorid.  The  bath  above  described, 
with  5^  pounds  of  salt  to  the  cubic  foot,  contains  not  quite  8  p.  c.  of  salt. 
It  will  thus  be  understood  why  in  some  cases  it  may  become  necessary  to 
increase  the  amount  of  salt  in  the  bath  in  order  to  augment  its  solvent 
power  for  the  dichlorid.  Both  by  cooling  and  by  dilution  with  water  the 
dichlorid  separates  in  the  form  of  a  white  heavy  crystalline  powder,  which 
is  readily  converted  by  simple  contact  with  metallic  iron  into  pure  crys- 
talline copper. 

In  treating  copper  ores  which  contain  no  sulphur  and  consequently  form 
no  soluble  sulphate  in  roasting,  the  loss  of  the  bath  in  chlorine  may  be  sup- 
plied by  adding,  from  time  to  time,  small  portions  of  protosulphate  of  iron, 
or  still  better  by  passing  over  or  through  the  liquid  in  the  stirring  or  leach- 
ing vats,  as  already  described  (page  16),  a  current  of  sulphurous  acid  gas. 
This,  being  absorbed,  converts  the  separated  hydrous  peroxyd  of  iron 
into  a  mixture  of  protosulphate  and  protosulphite  of  iron,  at  the  same  time 
liberating  the  combined  chlorine  of  the  oxychlorid  in  the  form  of  soluble 
protochlorid. 

As  the  protoxyd  of  copper  is  a  comparatively  feeble  base,  the  solutions  of 
the  protochlorid  are  readily  decomposed  by  the  oxyds  of  zinc  and  lead, 
which  are  often  present  in  roasted  ores.  These  cause  the  separation  from 
the  solutions  of  a  green  insoluble  oxyehlorid  composed  of  oxyd  and  proto- 
chlorid of  copper,  chlorid  of  zinc  or  of  lead  being  formed  at  the  same  time. 


32 

In  the  presence  of  an  excess  of  protochlorid  of  iron  this  oxychlorid  of 
copper  is  immediately  dissolved,  as  oxyd  of  copper  would  be,  but  in  the  re- 
action a  certain  amount  of  chlorine  is  consumed  in  forming  the  chlorids  of 
zinc  and  lead.  An  excess  of  oxyd  of  copper  also  unites  with  protochlorid 
of  copper  to  form  this  oxychlorid,  so  that  in  leaching  ores  charged  with  oxyd, 
the  protochlorid  of  copper  formed  is  at  first  retained  in  a  form  insoluble  in 
water  and  in  brine,  but  as  it  is  completely  dissolved  in  an  excess  of  proto- 
chlorid of  iron,  this  reaction  gives  rise  to  no  difficulty  in  working. 

In  like  manner  carbonate  of  lime,  though  without  action  on  solutions  of 
protochlorid  of  iron  below  212°  F.  readily  decomposes  protochlorid  of 
copper  at  140°  F.,  with  separation  of  a  similar  oxychlorid,  which  requires 
protochlorid  of  iron  to  redissolve  it.  In  this  way  the  presence  of  carbonate 
of  lime  in  copper  ore  indirectly  causes  a  loss  of  protochlorid  of  iron,  which 
must  be  supplied  in  one  of  the  ways  already  set  forth.  The  action  of  car- 
bonate of  magnesia  is  similar  to  that  of  the  carbonate  of  lime.  Neither 
these  substances  nor  the  oxyds  of  lead  or  zinc  separate  the  copper  from  the 
dichlorid. 

In  the  precipitation  of  the  copper  by  metallic  iron  28  parts  of  this  metal 
unite  with  35.5  parts  of  chlorine,  and  in  so  doing  separate  from  a  solution 
of  the  protochlorid  31.75  of  copper,  and  from  the  dichlorid  twice  that 
amount.  Hence  to  obtain  100  parts  of  copper  from  the  first  requires  88.2 
parts,  and  from  the  second  44.1  parts  of  iron,  while  from  solutions  in  which 
one-half  the  copper  exists  as  protochlorid  and  one-half  as  dichlorid  the 
amount  of  iron  required  will  be  the  mean  of  these  two,  or  about  66  parts 
for  100  of  copper. 

In  the  roasting  of  sulphuretted  copper  ores  the  greater  part  of  the  copper 
(apart  from  the  sulphate)  is  obtained  as  protoxyd,  besides  a  variable  amount 
of  dinoxyd,  sometimes,  according  to  Plattner,  as  much  as  20  or  30  p.  c.  of 
the  copper.1  Such  a  mixture  when  treated  in  the  bath  gives  rise,  of  course, 
to  a  correspondingly  large  amount  of  dichlorid,  which  is,  however,  gen- 
erally nearly  counterbalanced  by  the  protochlorid  resulting  from  the 
reaction  between  the  sulphate  of  copper  and  the  salt  of  the  bath,  so  that 
the  proportion  of  iron  required  to  separate  100  parts  of  copper  from  the 
solution  of  such  roasted  ores  varies  from  60  to  70  parts.  Hence  the  present 
process  presents,  in  this  respect,  a  great  economy  over  the  ordinary  wet 
methods  in  which  the  precipitation  of  100  parts  of  copper  requires  100  and 
often  1 20  or  more  parts  of  metallic  iron. 

1  In  some  cases  we  have  found  in  such  roasted  ores  a  portion  of  sulphate  of  dinoxyd  of 
copper.  This  remains  when  the  ordinary  sulphate  (of  protoxyd)  has  been  removed  by 
water,  and  may  be  dissolved  from  the  residue  by  a  hot  solution  of  common  salt,  by  which 
this  insoluble  sulphate  is  converted  into  dichlorid.  Some  copper  ores  of  15  or  20  p.  c.  have 
yielded  as  much  as  one  per  cent,  of  copper  in  this  form,  which  is  of  course  readily  soluble 
in  the  protochlorid  of  iron  bath. 


33 

A  solution  of  protochlorid  of  copper  when  mixed  with  salt  not  only  has 
the  power  of  chloridizing  and  dissolving  metallic  copper,  as  already  de- 
scribed, but  readily  takes  up  the  copper  from  sulphuretted  ores,  such  as  the 
vitreous  and  variegated  species,  and  from  copper  matte  or  regulus,  with 
separation  of  sulphur  and  formation  of  dichlorid.  This  reaction  may,  in 
some  cases,  be  taken  advantage  of  by  causing  a  hot  solution  nearly  satu- 
rated with  salt  and  holding  protochlorid  of  copper,  to  filter  through  a  layer 
of  such  ore  or  regulus  in  coarse  powder.  The  metal  is  rapidly  taken  up,  and 
solutions  obtained  in  which  the  whole  of  the  copper  is  present  as  dichlorid. 
In  this  way  an  additional  amount  of  copper  is  dissolved  and  may  be  separated 
in  the  metallic  state  with  very  little  cost.  The  66  parts  of  iron  required 
to  precipitate  100  of  copper  from  the  ordinary  solutions  of  mixed  proto- 
chlorid and  dichlorid  will  separate  from  solutions  of  pure  dichlorid  150 
parts  of  copper. 


V.    PATENT  SPECIFICATION. 

Letters  patent  for  the  process  above  described  were  granted  to  T.  Sterry 
Hunt  and  James  Douglas,  Jr.,  in  1869,  in  the  United  States,  Great  Britain 
and  Canada,  the  date  of  the  United  States  patent  being  Feb.  9,  1869. 
The  nature  of  the  process  and  the  mode  of  applying  it  having  been  fully 
set  forth  in  the  preceding  pages,  it  will  be  sufficient  to  give  the  following 
extracts  from  the  specification: 

"We  do  not  claim  the  use  of  any  particular  form  of  furnace,  nor  of  any 
special  arrangement  for  calcining,  lixiviating  or  precipitating,  reserving  to 
ourselves  the  choice  of  the  best  forms  of  apparatus  for  these  purposes, 
neither  do  we  claim  the  use  of  protosalts  of  iron  otherwise  than  in  solution, 
nor  the  use  of  perchlorid  or  other  persalts  of  iron,  nor  yet  the  use  of  sul- 
phurous acid  save  and  except  in  connection  with  protosalts  of  iron,  as 
already  set  forth. 

"  What  we  claim  as  our  invention  is: 

"  I.  The  use  and  application  of  a  solution  of  neutral  protochlorid  of  iron, 
or  of  mixtures  containing  it,  for  the  purpose  of  converting  the  oxyd  or 
suboxyd  of  copper,  or  their  compounds,  into  chlorids  of  copper. 

"  II.  The  use  of  sulphurous  acid  for  the  purpose  of  decomposing  the 
oxychlorid  of  iron  formed  in  the  preceding  re-action. 

"  III.  The  use  of  a  process  for  the  purpo'se  of  extracting  copper  from  its 
naturally  or  artificially  oxydized  compounds  by  the  aid  of  the  first,  or  the 
first  and  second  of  the  above  reactions,  substantially  in  the  manner  already 
set  forth." 


34 

VI.    WHAT  ORES  OF   COPPER   MAY  BE  TREATED    BY  THIS  PROCESS. 

The  forms  in  which  copper  occurs  in  nature  may  be  conveniently  grouped 
in  three  classes  to  each,  of  which,  under  certain  conditions,  the  Hunt  and 
Douglas  process  may  be  advantageously  applied. 

In  the  first  class  may  be  included  the  various  sulphuretted  ores,  such  as 
copper  pyrites  (often  mixed  with  iron  pyrites)  and  the  variegated  and 
vitreous  sulphurets,  all  of  which  are  readily  oxydized  by  calcination.  In 
addition  to  these  are  the  fahl-ores,  which  contain  besides  sulphur,  arsenic 
and  antimony.  These  objectionable  elements  by  calcination  are  either  ex- 
pelled or  rendered  insoluble.  All  the  above  named  ores  yield  their  copper 
after  oxydation  to  the  Hunt  and  Douglas  bath.  The  question  of  the  com- 
parative fitness  of  this  method  for  rich  and  poor  ores  has  already  been 
discussed  on  page  6. 

In  the  second  class  are  included  the  oxydized  compounds  of  copper,  such 
as  the  red  and  black  oxyds,  the  green  and  blue  carbonates,  salts  like  the 
oxychlorid  and  also  silicates  of  copper  like  chrysocolla.  All  of  these  are 
readily  attacked  by  the  bath  without  previous  calcination;  but  in  the  case 
of  the  red  or  dinoxyd,  as  already  explained  above,  it  should  either  be 
mixed  with  protoxyd  ores  or  in  part  converted  into  protoxyd  by  a  slight 
calcination  in  order  to  render  the  copper  wholly  soluble.  The  carbonates 
of  copper,  which  are  readily  dissolved  in  the  bath,  give  off  their  carbonic 
acid  so  as  to  cause  frothing,  to  prevent  which  it  may  be  well  to  give  them  a 
slight  calcination  or  roasting.  Heating  them  to  low  redness  in  a  kiln  or 
furnace  for  a  few  minutes  will  be  sufficient  to  convert  the  carbonates  into 
protoxyd. 

The  common  silicate  of  copper  called  chrysocolla,  readily  gives  up  its 
copper  to  the  bath  of  protochlorid  of  iron  and  salt,  so  that  its  treatment, 
whether  alone  or  mixed  with  other  ores,  presents  no  difficulty.  A  peculiar 
ore  which  is  now  treated  successfully  by  this  process  at  Phoenix ville,  Penn., 
is  a  hydrated  silicate  of  oxyd  of  copper  with  magnesia,  alumina  and  per- 
oxyd  of  iron,  containing  when  pure  about  13  p.  c.  of  copper.  This  mineral, 
which  may  be  described  as  a  copper-chlorite,  is  readily  and  completely 
decomposed  by  acids  but  is  not  attacked  by  the  bath  of  protochlorid  of  iron. 
To  extract  the  copper  it  is  treated  as  follows:  The  crude  ore,  which  is 
mixed  with  clay  and  sand  and  carries  from  3.0  to  6.0  p.  c.  of  copper,  is 
heated  to  low  redness  for  some  hours  in  large  vertical  muffles  each  holding 
15,000  Ibs.,  having  been  previously  mixed  with  one-tenth  its  weight  of  coal 
in  coarse  powder,  by  which  the  combined  oxyd  of  copper  is  reduced  to  the 
metallic  state.  This,  on  withdrawing  the  heated  charge,  is  at  once  oxydized 
by  the  air,  yielding  a  mixture  of  protoxyd  and  dinoxyd  of  copper,  which 
are  readily  and  completely  removed  by  the  subsequent  operation  of  leach- 
ing with  the  Hunt  and  Douglas  bath.  The  copper  is  chiefly  dissolved  in 


35 

the  form  of  dichlorid,  as  is  shown  by  the  fact  that  not  more  than  50  parts  of 
metallic  iron  are  required  to  precipitate  100  parts  of  copper  from  the 
solution. 

The  third  class  includes  the  deposits  of  native  or  metallic  copper,  which 
in  almost  all  instances  are  most  advantageously  treated  by  mechanical 
means.  In  those  rare  cases,  in  which  the  copper  is  too  finely  divided  to 
be  thus  profitably  extracted,  it  will  be  found  that  by  careful  calcination 
at  a  low  red  heat  it  may  be  oxydized  so  as  to  become  soluble  in  the  pro- 
tochlorid  of  iron  bath.  In  this,  as  in  all  other  cases  of  non-sulphuretted 
ores,  it  is  as  already  explained  (page  16)  indispensable  to  supply  the  loss 
of  chlorine  by  the  use  of  sulphurous  acid  fumes,  or  by  the  addition  from 
time  to  time  of  a  protosalt  of  iron. 

The  presence  of  carbonate  of  lime  or  carbonate  of  magnesia  in  any  ore 
is  objectionable,  since  as  already  explained  (page  32),  it  decomposes  the 
protochlorid  of  copper  and  thus  indirectly  precipitates  the  iron  from  the 
bath.  The  action  of  oxyds  of  lead  and  zinc,  which  come  from  the  roasting 
of  blende  and  galena  when  these  are  present  in  the  ore,  produces  a  similar 
effect.  When  not  present  in  too  large  quantities,  the  effect  of  all  these 
substances  may  be  corrected  by  careful  roasting,  which  forms  a  large  pro- 
portion of  sulphates,  or  by  the  use  of  sulphurous  fumes,  but  ores  containing 
much  carbonate  of  lime  or  carbonate  of  magnesia  are  not  adapted  to  treat- 
ment by  this  or  any  other  wet  process. 


VII.    PRACTICAL  WORKING  OF  THE  PROCESS. 

The  Hunt  and  Douglas  process,  after  some  experimental  trials,  was  first 
worked  continuously  for  a  year  in  1872-73  at  the  Davidson  Mine  in  ]STorth 
Carolina,  under  the  direction  of  the  Messrs.  Clayton.  The  ore,  a  pyritous 
copper  in  a  slaty  gangue,  was  dressed  up  to  five  or  six  per  cent.,  crushed  to 
pass  through  a  sieve  of  forty  meshes  to  the  linear  inch,  roasted  in  three- 
hearth  reverberatory  furnaces  so  as  to  contain  about  one-fourth  its  copper 
as  sulphate,  and  treated  in  stirring  vats  in  charges  of  3000  Ibs.  The  loss 
of  copper  in  the  residue  was  found  to  be  from  0.3  to  0.5  p.  c.,  and  the  bath 
maintained  its  strength  in  chlorid  of  iron  without  the  use  of  copperas  or 
sulphurous  acid.  The  amount  of  iron  consumed  was  equal  to  70  p.  c., 
and  the  salt,  to  supply  unavoidable  losses,  to  25  p.  c.  of  the  copper  pro- 
duced. These  details  are  from  a  letter  from  the  manager  of  the  works, 
Mr.  James  E.  Clayton,  published  in  the  Engineering  and  Mining  Journal 
for  July,  1873,  from  which  it  appears  that  the  entire  cost  of  producing  cement 
copper  from  the  dressed  ore  of  5J  p.  c.  was  estimated  to  be  three  and  two- 
thirds  cents  a  pound. 


36 

This  mine  was  subsequently  abandoned,  and  the  same  proprietors  in  1874 
erected  works  with  six  calcining  furnaces  for  the  treatment  of  twelve  tons 
of  pyritous  ore  daily  by  this  process  at  the  Ore  Knob  mine  in  Ashe  County, 
North  Carolina.  Up  to  the  first  of  January,  1875,  over  200  tons  of  copper 
had  there  been  made  by  this  process.  In  the  report  bearing  that  date  of 
the  directors  of  the  Ore  Knob  Co.,  James  E.  Tyson  of  Baltimore,  president, 
it  is  said,  "  From  the  data  furnished  by  the  superintendent  in  his  Report 
from  the  mine,  and  a  careful  estimate  made  here,  we  find  the  cost  of  making 
copper,  mining,  and  all  expenses  included,  to  be  less  than  eight  cents  a 
pound." 

These  works  were  soon  after  enlarged  to  nearly  three  times  their  former 
capacity,  but  in  sinking  below  the^  water-line  in  the  mine  the  ore,  hitherto 
free  from  lime,  was  found  to  contain  30  p.  c.  or  more  of  carbonate  of  lime 
with  some  magnesia.  The  direct  treatment  of  such  an  ore  by  any  moist 
process  was  impracticable,  and  the  reduction  works  were  accordingly  sus- 
pended pending  the  erection  of  dressing-works  in  which  it  is  proposed  to 
concentrate  the  ore  by  crushing  and  washing,  removing  thereby  the  car- 
bonate of  lime  of  the  gangue.  The  concentrating  machinery,  as  we  are 
informed  by  the  managing  director  of  the  Ore  Knob  Copper  Co.,  Mr. 
James  E.  Clayton,  will  be  in  operation  in  June,  1876,  when  it  is  proposed 
to  recommence  at  once  the  treatment  of  the  purified  ores  by  the  Hunt  and 
Douglas  process. 

Reduction-works  are  now  in  successful  operation  at  Phoenixville,  Penn- 
sylvania, where  copper  ores  of  two  kinds  are  treated  by  the  Hunt  and 
Douglas  process,  the  first  of  which  is  a  magnetic  iron  ore  from  Berks  Co., 
Penn.,  containing  about  3  p.  c.  of  copper,  chiefly  as  copper  pyrites,  mixed, 
however,  with  a  little  carbonate  and  silicate  of  copper.  This  ore,  of 
which  20,000  Ibs.  are  treated  daily,  is  crushed  so  as  to  pass  through  a  sieve 
of  seven  meshes  to  the  linear  inch,  roasted  as  already  explained  on  page 
11,  and  subsequently  treated  by  leaching.  The  residue,  which  contains 
about  0.5  p.  c.  of  copper,  is  a  rich  iron  ore  which  is  used  for  lining  pud- 
dling furnaces.  The  second  ore  is  the  peculiar  hydrated  silicate  described 
on  page  34,  of  which  15,000  Ibs.  are  treated  daily.  The  leached  residues 
of  this  do  not  retain  over  0.3  p.  c.  of  copper. 

The  works  of  the  Stewart  Reduction  Co.,  at  Georgetown,  Colorado,  in 
which  this  process  is  applied  to  mixtures  of  silver  and  copper  ores,  will  be 
again  referred  to. 


37 


VIII.    TREATMENT  OF  SILVER  AND  GOLD  ORES. 

The  use  of  soluble  compounds  of  copper  as  an  agent  in  treating  silver 
ores  and  rendering  them  fit  for  amalgamation,  has  long  been  known,  and  is 
the  basis  of  the  Mexican  patio  process  and  its  modifications,  as  well  as  of 
the  Washoe  process  now  largely  employed  in  the  west.  The  theory  of  the 
action  of  the  copper  salts  in  the  first  of  these  methods,  where  the  materials 
are  exposed  for  a  long  time  to  the  action  of  the  air,  is  still  somewhat  ob- 
scure. In  the  Washoe  method  sulphate  of  copper  and  common  salt  are 
added  together  to  the  ground  ore  mixed  with  water,  and  from  these  by  the 
reactions  which  take  place  in  the  pans,  dichlorid  of  copper  is  soon  formed. 
This  substance  dissolved  in  brine  is  used  directly  with  advantage  in  the 
treatment  of  silver  ores  by  Janin  and  by  Kroncke.  From  the  results  of 
various  experimenters,  it  is  clear  that  solutions,  both  of  protochlorid  and 
dichlorid  of  copper,  mixed  with  common  salt,  when  at  an  elevated  temper- 
ature, effect  a  complete  chlorination  of  sulphuretted  and  arsenical  silver 
ores,  or  at  least  render  them  susceptible  of  ready  and  complete  amalga- 
mation. 

The  use  of  the  chlorids  of  copper  as  hitherto  applied,  presents,  however, 
several  difficulties:  1st.  The  sulphate  of  copper  from  which  they  are  gen- 
erally prepared  is  costly,  and  in  some  places  difficult  to  procure;  2d.  Pro- 
tochlorid of  copper  is  readily  decomposed  and  separated  from  hot  solutions 
as  an  insoluble  oxychlorid  by  the  carbonate  of  lime  often  found  with  the 
ores;  3d.  Solutions  of  dichlorid  of  copper  in  brine  very  readily  absorb 
oxygen  from  the  air,  forming,  besides  protochlorid  of  copper,  also  an  insolu- 
ble oxychlorid.  These  oxychlorids  are  without  action  on  silver  ores, 
though  they  attack  the  mercury  when  amalgamation  is  attempted  simul- 
taneously with  the  treatment  by  copper  salts,  forming  an  insoluble  chlorid 
of  this  metal,  and  thereby  causing  a  considerable  loss. 

To  meet  these  objections  there  is  needed  a  cheap  and  ready  method  of 
preparing  the  chlorids  of  copper,  and  a  simple  means  of  preventing  their 
precipitation  in  inert  or  noxious  forms  by  the  action  of  the  air  or  carbonate 
of  lime.  It  will  be  apparent  from  the  preceding  account  of  the  chemistry 
of  the  Hunt  and  Douglas  copper  process,  that  the  use  of  a  heated  solu- 
tion of  protochlorid  of  iron  and  salt,  aided  by  sulphurous  acid,  for  the  solu- 
tion of  the  oxydized  compounds  of  copper,  meets  the  conditions  of  the 
problem  in  the  following  manner: 

1st.  The  Hunt  and  Douglas  bath  gives  readily  and  cheaply  strong 
solutions  of  the  mixed  protochlorid  and  dichlorid  of  copper  wherever  car- 
bonates, oxyds,  or  calcined  sulphuretted  ore  of  this  metal  can  be  had. 


38 

2d.  It  dissolves  the  oxychlorids  of  copper,  by  whatever  means  produced, 
changing  them  into  a  mixture  of  protochlorid  and  dichlorid  of  copper,  and 
thus  prevents  any  deterioration  of  the  copper  solution  by  the  action  of  the 
air  or  of  carbonate  of  lime. 

The  Hunt  and  Douglas  bath  may  be  advantageously  applied : l 

I.  To  effect  more  cheaply  and  more  completely  the  chlorination  and 
the  amalgamation  of  such  silver  ores  as  are  now  treated  in  the  raw  state 
with  chemicals,  as  they  are  called,  —  that  is  to  say,  sulphate  or  chlorid  of 
copper  with  common  salt. 

II.  To  chlorinate  such  silver  ores  as  have  been  calcined  without  the 
addition  of  salt, 

III.  To  complete  the  chlorination  of  silver  ores  which  have  been  par- 
tially chlorinated  by  calcining  with  salt,  thus  securing  a  much  more  com- 
plete extraction  of  the  silver  than  has  hitherto  been  attained. 

In  all  of  these  cases  it  will  be  understood  that  some  oxydized  form  of 
copper,  such  as  carbonate,  native  oxyd  or  calcined  sulphuretted  ore,  is  to 
be  added,  unless  it  is  already  present  in  the  silver  ore  to  be  treated.  It  may 
be  added  even  in  large  quantities  with  advantage,  and  from  the  solutions 
charged  with  copper  a  portion,  or  the  whole  of  this  metal  may  be  precipi- 
tated from  time  to  time  by  metallic  iron  as  cement  copper. 

In  localities  where  salts  of  iron  are  not  readily  obtained,  and  where  sul- 
phur ores  are  abundant,  it  will  be  found  that  by  passing  sulphurous  acid 
gas  into  or  over  a  solution  of  salt  holding  pulverized  oxyd  or  carbonate  of 
copper  in  suspension,  a  solution  of  dichlorid  of  copper  will  be  readily 
formed,  and  this  reaction  may  be  rendered  available  for  the  treatment 
of  silver  ores.  By  precipitating  the  copper  solution  thus  obtained  with 
metallic  iron,  protochlorid  of  iron  is  at  once  readily  and  cheaply  obtained. 

Silver  ores  chlorinated  by  the  Hunt  and  Douglas  bath,  may  be  subse- 
quently treated,  either  by  dissolving  the  silver  from  the  washed  residues  by 
a  solution  of  hyposulphite  or  of  chlorid  of  sodium,  or  by  amalgamation. 
The  use  of  mercury  is  to  be  preferred  for  ores  holding,  besides  silver,  a 
portion  of  gold.  Such  ores  should  be  treated  with  the  bath  in  the  raw  state, 
or  after  simple  calcination,  roasting  with  salt  being  for  them  objectionable. 

United  States  letters  patent  (No.  151,763)  for  the  use  of  the  Hunt  and 
Douglas  bath  of  protochlorid  of  iron  and  common  salt,  conjointly  with 
sulphurous  acid,  for  the  treatment  of  silver  ores,  or  silver  and  gold  ores, 
mixed  with  oxydized  ores  of  copper,  were  granted  June  9,  1874,  to  James 
Douglas,  Jr.,  Thomas  Sterry  Hunt  and  James  Oscar  Stewart.  This  pro- 
cess has  now  been  most  successfully  applied  for  more  than  a  year  on  a  large 
scale  in  the  working  of  silver  ores  by  Mr.  Stewart,  who  will  publish  in  the 

1  Later  observations  show  that  this  process  may  be  advantageously  applied  to  the  treat- 
ment of  the  tellurids  of  silver  and  gold. 


39 

course  of  the  summer  of  1876  a  detailed  description  of  the  method  as 
adapted  by  him  to  various  kinds  of  silver  ores.  Copies  of  this  (and  also 
of  the  present  pamphlet)  may  be  had  by  addressing  J.  Oscar  Stewart, 
Georgetown,  Colorado. 


For  further  information  concerning  the  Hunt  and  Douglas  process  as 
applied  to  copper  extraction,  address 

JAMES  DOUGLAS,  JR., 

Phcenixville,  Penn., 
or 

T.   STERRY  HUNT, 

Boston,  Mass. 
May,  1876, 


RETURN    CIRCULATION  DEPARTMENT 
^    202  Main  Librarv 


HOME  USE 

3 

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DUE  AS  STAMPED  BELOW 

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W-C.  BERKELEY 

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FORM  NO.  DD6 


,  CA  94720 


